A week of clothes is the easy part of a personal-item-only trip. Map Happy's author rolled five days of clothing into a cube that took up about 5.5 of a 20-liter bag's liters. The hard limit is the bag's outside measurement. Frontier counts that measurement including handles, wheels and straps, and it is the figure a gate agent checks. The packing below takes one evening, trial pack included, and ends with a bag that has been measured full rather than empty.

One caveat before starting. The EU has agreed to make a larger cabin bag free with a standard fare, but Euronews puts the earliest start at October 23, 2027. It covers only flights to and from the EU. For trips booked now, the under-seat bag is the whole allowance.

What goes in

  • An under-seat bag of 18 to 25 liters

    The range Map Happy recommends for personal-item-only travel. It must also meet the airline's outside dimensions when full.

  • One compression packing cube

    Holds the rolled clothes. No source here publishes how much compression saves, so judge it by whether the bag closes.

  • A clear, quart-sized resealable bag

    For liquids in containers of 3.4 oz or less, the rule KAYAK summarizes for TSA screening.

  • Travel-size containers or solid bars

    Shampoo bars and solid deodorant stay out of the liquids bag entirely.

  • A tape measure

    For the full-bag measurement in the last step.

Brand-name cubes and toiletry bags are a matter of taste. None of the published sources here gives sizes or capacities for a specific model, so none is recommended.

Loading it, in order

  1. Write down the airline's limit

    Frontier's official bag FAQ sets 14" H x 18" W x 8" D. Its bag options page allows one per passenger, per direction, under the seat. Ryanair's free bag is 40 x 30 x 20 cm according to Baggage Policies, which is shorter. Worked when: the number for every leg is on paper.

  2. Lay out the clothes to a count

    TripGazer's count for one to two weeks is 4 to 5 tops, 2 bottoms, 5 to 6 pairs of underwear and socks, one sleep set, one light layer and one packable rain jacket. It assumes one laundry stop for any trip longer than a week. Worked when: the pile matches the count and nothing extra is on the bed.

  3. Choose the outfit for the plane

    Wear the bulkiest layer, the walking shoes and the jacket. Map Happy's author wore sweater, scarf and overcoat aboard. Frontier lists coats among items exempt from the allowance. Cap shoes at two pairs. Worked when: the heaviest items are off the pile.

  4. Roll the clothes into the cube

    TripGazer and ScanFlyGo both advise rolling over folding. Neither publishes a space figure, so the case for it rests on the cube closing. Worked when: the cube zips and compresses flat.

  5. Fill the liquids bag

    Decant into 3.4 oz containers and seal them in the quart bag. Swap whatever can become a bar. Worked when: the quart bag closes without strain.

  6. Gather the electronics

    Pack phone, charger, power bank and earbuds. Bring both USB-A and USB-C cables. Rick Steves forum posters note some aircraft have only USB-A ports. Power banks must stay in cabin luggage, per ScanFlyGo. Worked when: each device has a cable that fits it.

  7. Load the bag

    Cube first, against the back panel. Electronics alongside. Liquids bag where it lifts out without unpacking. Passport, cards and all prescription medication go last, on top, the priorities the Rick Steves forum agreed on. Worked when: documents are reachable with the bag under a seat.

  8. Measure it full

    Zip it, then measure depth with the straps included. An empty bag that fits the rule says nothing about a full one. Worked when: every dimension is at or under the limit from step one.

The strongest objection is that a paid carry-on removes all of this. It does, and Frontier's FAQ says the cheapest time to buy one is at booking. Prices rise at the airport and again at the gate. A trip that fails step eight should buy the bag then. The fee difference between the two is set out on the cost of each bag. For a week with one laundry stop, though, the pile in step two fits.

When it will not close, or will not fit

Take out the second pair of shoes or one bottom and measure again. Do not gamble at the gate. Trecklist puts oversize personal-item gate fees on European ultra-low-cost carriers at about €50 to €100. Baggage Policies reports that Ryanair raised its staff bonus for catching oversized bags to €2.50 per bag in 2026.

Convert shampoo and deodorant to bars, or switch to a 2-in-1 shampoo and conditioner in one refillable bottle, as Always Pack Tissues suggests. Hotels often supply the rest.

That is the laundry stop TripGazer builds in. None of the sources here publishes a price for one, so check the hostel's or laundromat's own listing before counting on it. The other route is Always Pack Tissues' 'pack and ditch' method: bring old underwear and socks and discard them along the way.

A bag measured full at home is the only one worth taking to an airport. If it fails the sizer anyway, the gate fee on Spirit, Frontier and Allegiant is the number to know before boarding.