Carry-On Packing Mistakes That Cost Travellers Money

If you’ve ever booked a ridiculously cheap flight and then somehow paid almost the same amount again at the airport, your carry on bag was probably involved. The biggest carry on packing mistakes cost travellers money because airlines make their rules intentionally tight, inconsistently enforced and expensive to fix at the gate. What looks fine at home can suddenly become a £50 problem five minutes before boarding.

The good news is that most of these costs are completely avoidable once you know where people go wrong. Here’s what actually causes travellers to lose money and how to make sure your cheap flight stays cheap.

Assuming Carry On Rules Are The Same Everywhere

One of the most expensive assumptions travellers make is thinking a carry on bag is a universal size. It isn’t.

Low cost airlines set their own limits and they change them quietly. A bag that passed with one airline last month might be flagged by another tomorrow. According to a 2024 survey by the European Consumer Organisation, 42% of passengers were unsure of their airline’s carry on size rules before travelling. That uncertainty is exactly what airlines profit from.

Always check the specific allowance for your exact ticket type, not just the airline in general. Basic fares often allow less than you think.

Packing For Space Instead Of Weight

Many travellers focus on whether their bag looks small enough, completely forgetting that weight limits exist. And weight is where airlines love to catch people out.

A packed carry on can easily go over the limit even if it fits the size checker. Portable chargers, shoes, toiletries and jackets add up fast. In a 2023 aviation report, over 30% of gate checked carry on bags were flagged due to weight rather than size.

If your airline has a weight limit, assume they might actually check it. Use a luggage scale at home and leave a buffer. Being 1kg over can be the difference between boarding calmly and paying on the spot.

Bringing A Bag That Looks Too Big Even If It Isn’t

Airlines rarely measure every bag. They judge first by sight.

Structured bags with hard edges, wheels, and tall frames draw attention even if they technically meet the rules. Softer bags that compress slightly are far less likely to be questioned.

This is why 2 people with the same allowance can have very different experiences at the gate. If your bag looks oversized, you are more likely to be stopped. And once a staff member is looking closely, they usually find something to charge you for.

Forgetting That Basic Fares Often Exclude Proper Carry On Bags

Many cheap tickets include only a small personal item. Not a cabin suitcase. 

This is one of the most common money draining mistakes we see. Travellers assume carry on means a bag in the overhead locker, when in reality it means something that fits under the seat in front of you.

If your ticket only includes a personal item and you turn up with a full size cabin bag, the airport price will always be higher than adding it during booking.

Overpacking Just In Case

Packing extra outfits, extra shoes or things you might use is a fast way to turn a free carry on into a paid bag.

Overpacking leads to bulging bags that fail size checks, tip over weight limits or simply attract attention. Ironically, the more you try to be prepared, the more likely you are to pay.

Most trips require far less than people think. Washing clothes once, wearing heavier items on the plane and skipping unnecessary extras saves space and stress.

Ignoring Liquids Rules Until Security

Liquids are still one of the easiest ways to lose money or time. Oversized toiletries can force you to repack at security and dump products you paid for.

Keeping liquids minimal and compliant avoids panic decisions that often lead to paid baggage or rushed purchases airside.

Thinking Gate Fees Will Be Reasonable

They won’t be.

If your carry on bag is rejected at the gate, you are paying the maximum fee with no negotiation. Gate fees are designed to hurt. They are consistently higher than booking fees and sometimes higher than checked baggage purchased in advance.

Once you’re there, your options are limited. Airlines know that and price accordingly.

How To Protect Your Flight Deal

Carry on bags are one of the biggest ways airlines recover money on cheap fares. That doesn’t mean you can’t win. It just means you need to play by the real rules, not the advertised ones.

Choose flexible bags, pack lighter than you think you need, know your exact allowance and never assume staff will be lenient. The cheapest travellers are not the luckiest ones. They are the ones who prepared.

Because the best flight deal is the one that stays cheap all the way to the runway.

Book Flights With Secret Flight Club

Booking smart doesn’t stop with packing. Secret Flight Club alerts members to genuinely cheap flights before everyone else sees them, giving you more choice on fares, airlines and baggage options from the start. When you begin with a better deal, avoid hidden carry on costs and know the rules in advance, you keep more money where it belongs — in your travel budget, not the airline’s pocket.