You Found a Cheap Flight. Now Watch Out for the 7 Things That Can Make It Expensive Again.

The fare is the number airlines advertise. These are the seven they don't, and the simple packing change that takes most of them off the bill.

SummaryBag fees, gate checks, “personal item only” fares and a suitcase that won't close on the way home can add $100 or more to a cheap round trip. Most of them go away if everything fits in one carry-on. Our deals editor explains each one, and the compression kit she now packs with.

By Megan RossTravel Deals Editor

Updated Oct 27, 20267 min read

The fare is only the first number on the bill.

Last spring I found a $97 round trip to Denver. I took a screenshot and sent it to three friends with too many exclamation points. By the time I got home, that same trip had cost me more than twice as much, and I hadn't paid for a single meal yet.

Round-trip fare$97

Checked bag, outbound$45

Checked bag, return$45

Duffel bag bought on the trip (suitcase wouldn't close)$38

What the “cheap” flight actually cost$225

I track fares for a living, and I had been watching the wrong number. A few weeks later a flight attendant I was interviewing showed me how she packs a week into a carry-on: clear vacuum bags and a pump the size of a lipstick case. The kit was called SpaceMax. I bought one, mostly to prove it wouldn't work.

That was five trips ago. I haven't checked a bag since, and I haven't paid a bag fee since either.

The airlines aren't hiding these costs, exactly. They're just not in the big number you see first. So here are the seven I now check before I book, and what I do about each one.

One honest note first: I bought my own kit. Vacuum bags make clothes smaller, not lighter. If your airline weighs carry-ons, you still need to watch the scale.

Hidden cost 01 · Bag fees

Suitcase being placed on the scale at an airport bag drop — The fee you pay on the way out, and again on the way home.

1. The checked bag fee, and you pay it twice

Most cheap fares are cheap because the suitcase isn't included. When we see a deal, we tend to price the bag once, in our heads, and move on.

But you pay it in both directions. On the big US airlines, the first checked bag now costs about $45 to $50 each way. That's $90 to $100 per person for one round trip. For a family of four flying home for the holidays, it can be more than one of the tickets.

The fix isn't packing less. It's packing smaller. With the bulky pieces in SpaceMax bags, a week of clothes fits in a carry-on, and the bag fee drops to zero in both directions.

Round trip, one checked bag: about $90 to $100 per person on major US airlines in 2026. Family of four: $360 to $400.

Hidden cost 02 · The gate

2. The carry-on that's “too full” at the gate

Your carry-on is free, so you fill it to the last inch. Then it bulges, the zipper strains, and it won't slide into the metal sizer at the gate.

When a bag doesn't fit, agents can make you check it right there. On basic fares and budget airlines that can mean a checked-bag fee plus a gate fee, and some budget carriers charge close to $100 at the gate. Your bag ends up under the plane anyway.

The bulge usually isn't your stuff. It's the air in it. Sweaters, hoodies and jackets are mostly air. Take the air out and the same clothes lie flat, so the bag zips closed and keeps its shape.

Sizer rule: if the bag bulges, compress the bulky pieces first. Hoodies, sweaters and jackets shrink the most.

Overstuffed carry-on that will not fit the gate sizer — It's not the suitcase that's too big. It's the air in the clothes.

What a cheap round trip really costs
Cost	Checking a bag	One carry-on, packed with SpaceMax
Bag fee, outbound	✕ About $45–50	✓ $0
Bag fee, return	✕ About $45–50	✓ $0
Gate-check risk	✕ Overstuffed carry-ons get pulled	✓ Zips flat, fits the sizer
Carousel wait	✕ Often 20–40 min	✓ Walk straight out
Lost or delayed bag	✕ Possible	✓ Stays above your seat
Weight	= Same	= Same. Smaller, not lighter

Fees are typical first-bag fees on major US airlines in 2026 and vary by airline, route, fare and status.

Hidden cost 03 · The fare rules

Small backpack packed with flat SpaceMax bags and the cordless pump — A long weekend in a bag that fits under the seat.

3. The “personal item only” fare

The cheapest price in the search results is often a basic economy fare. On some airlines and routes, that fare includes only a personal item that fits under the seat in front of you. No full-size carry-on.

Most people find out at checkout or at the airport, then pay to upgrade or to add a bag. Either way, the savings that made you book are gone.

An under-seat backpack holds a lot more than you'd think once the clothes are compressed. An M bag takes jeans and two sweaters, an S bag takes the T-shirts, and the pump slides into a side pocket. That's a long weekend under the seat.

Before you book: check whether your fare includes a full-size carry-on. If it doesn't, pack for the under-seat bag from the start.

$45–50

first checked bag, each way, on major US airlines (2026)

30–60 sec

to flatten one SpaceMax bag with the cordless pump

~40

bags flattened on a single charge

Pack the whole trip in one carry-on

Every SpaceMax kit comes with the cordless pump and a mix of S, M and L bags. Pick the one that fits how you travel.

See the kits · From $59.99 →

Free US shipping on the Suitcase + Closet Kit and Family Kit · 60-day money-back guarantee

Hidden cost 04 · The trip home

4. The suitcase that won't close on the way home

Your bag closed fine when you left. A week later it's holding gifts, a few things you bought, and laundry that never folds as small as clean clothes.

Most packing tricks only work once, at home. Roll-up bags never get as flat the second time, there's no vacuum in a hotel room, and cheap vacuum bags often puff back up overnight because air gets back in through the zip, the valve or the film.

The SpaceMax pump is cordless, weighs 4.6 oz and charges with USB-C, so it travels with you. The night before your flight home, you repack every bag on the hotel bed in a few minutes. The bags seal at all three leak points, so they're still flat when you land.

SpaceLock 3-Seal: double zip, screw-down valve and two-layer film. Souvenirs still weigh what they weigh, so check your airline's weight limit.

Repacking SpaceMax bags with the cordless pump in a hotel room — Repacking on the hotel bed, the night before the flight home.

Hidden cost 05 · The second bag

Traveler buying an extra duffel bag at a tourist shop — The bag you never planned to own, and then have to pay to check.

5. The extra bag you buy at your destination

When the suitcase won't close, the usual fix is a cheap duffel from a gift shop or the airport. It feels like a small, smart purchase in the moment.

It rarely is. The duffel costs $30 to $60, and then it has to fly home too. Now you're paying to check a bag you didn't own a week ago, on a flight you booked because it was cheap.

When the clothes you brought are compressed, there's room left over for what you bring back. The extra things go into the space the air used to take up, and the duffel stays on the shop rack.

The second-bag spiral: $30 to $60 for the bag, plus $45 or more to check it home.

Hidden cost 06 · Lost luggage

6. The bag that doesn't land with you

A checked bag passes through belts, carts and baggage rooms, and on a cheap itinerary it often has a tight connection to make as well. Most bags arrive. Some don't.

When yours is delayed, the first day of the trip goes to buying a toothbrush, a charger and something to wear at resort prices, then filling out a claim. Getting that money back can take weeks, and it isn't always all of it.

A carry-on can't get lost in the baggage system, because it never goes into it. Everything you need is in the bin above your seat, and it gets off the plane when you do.

Tight connection? That's when checked bags are most likely to miss the flight. A carry-on makes every connection with you.

Traveler filling in a lost-bag claim at the airport — The first day of the trip, spent on a claim form.

Hidden cost 07 · Your time

Carry-on traveler walking past the baggage carousel to the exit — Off the plane, past the carousel, out the door.

7. The hour you lose after you land

Cheap flights often leave early and land late. The last thing you want after one is another wait, but that's exactly what a checked bag gives you.

Bag drop on the way out, then often 20 to 40 minutes at the carousel on arrival. Meanwhile the taxi line grows, ride prices climb, and the first evening of your trip shrinks to dinner at the hotel.

With one carry-on you walk off the plane and out the door. And between trips, the same SpaceMax bags clear the winter coats out of your closet, so the kit keeps working when you're not flying.

Carry-on only: no bag drop, no carousel. That's often 30 minutes or more back on every trip.

Why 10,000+ travelers choose SpaceMax

★★★★★ What travelers say about their first carry-on-only trips

Sarah holding the SpaceMax pump in a hotel room

★★★★★

I book the cheapest fare now, and actually keep the savings

“I always book basic economy, and I used to get caught every time. Last year I paid $65 at the gate because my carry-on wouldn't fit the sizer. A friend told me to try compression bags with a pump. Now a week of clothes fits in my backpack and a small carry-on, and nobody at the gate looks twice.”

No bag fees on her last three trips.

Sarah T.Denver, CO · Verified Buyer

Daniel holding the SpaceMax pump next to a packed suitcase

No more two days in the same shirt

“I travel for work most weeks. On a tight connection in Atlanta my checked bag didn't make it, and I gave a client presentation in the shirt I flew in. That's when I switched to carry-on only. The jackets and sweaters go in the L bags, and I repack in the hotel the night before I fly home.”

Hasn't checked a bag since spring.

Daniel K.Chicago, IL · Verified Buyer

Michelle with the SpaceMax pump and a bag of kids' clothes

The bag fees used to cost more than the kids' tickets

“We're a family of four and we fly to my parents' every Christmas. Last year the bags cost us almost $400 round trip. This year I packed each kid's clothes in their own small bag and everyone rolled a carry-on. I checked in on my phone and we walked straight to security.”

$0 in bag fees for a family of four.

Michelle R.Austin, TX · Verified Buyer

You Found a Cheap Flight. Now Watch Out for the 7 Things That Can Make It Expensive Again.

1. The checked bag fee, and you pay it twice

2. The carry-on that's “too full” at the gate

3. The “personal item only” fare

Pack the whole trip in one carry-on

4. The suitcase that won't close on the way home

5. The extra bag you buy at your destination

6. The bag that doesn't land with you

7. The hour you lose after you land

Why 10,000+ travelers choose SpaceMax

I book the cheapest fare now, and actually keep the savings

No more two days in the same shirt

The bag fees used to cost more than the kids' tickets

What's in every SpaceMax kit

The cheap flight, plus a checked bag

The cheap flight, one carry-on

Choose your SpaceMax kit

Travel Kit

Suitcase + Closet Kit

Family Kit

Try it on your next cheap flight

Keep the cheap flight cheap.