How to pack a carry-on

The pattern to notice: past seven days the numbers stop growing. You do not pack fourteen shirts for fourteen days, you pack seven and wash once. That single decision is what makes a two-week carry-on trip possible, and the kit that enables it weighs a few ounces - see the travel laundry kit.

The easy case, and the one where people most often over-pack because there is room. Three or four days needs one pair of shoes beyond what you are wearing, three or four tops, and two bottoms. You will wear the same trousers three times and nobody will notice.

For a trip this short, consider whether you need a full carry-on at all. A personal item bag at 18 x 14 x 8 holds a genuine long weekend, which means you board with nothing in the overhead bin - and on Basic Economy it means you pay nothing extra.

The standard case, and the one a 40-liter carry-on is effectively designed around. Six tops, three bottoms, a week of underwear and socks, one layer, and two pairs of shoes including the ones you fly in.

The thing that goes wrong here is outerwear. A coat takes the volume of four shirts, so wear it rather than packing it - and if it is genuinely too warm to wear, carry it over your arm, which no airline counts as baggage. That single move is worth more than any packing technique.

This is the point at which you stop packing more and start planning one wash. Ten days of clothes does not fit a carry-on; seven days plus a sink wash does, comfortably, and the kit is detergent sheets and a clothesline.

Plan the wash for a day you are staying put, because laundry and a travel day do not combine. The method is in the travel laundry kit - the step people skip is rolling each item in a dry towel before hanging it, which is what decides whether things are dry by morning.

Cold weather roughly halves what fits, because a coat, a fleece and boots take the volume of most of a summer week. The three techniques that work:

1. Wear the bulkiest items on the plane. Coat, boots, the heaviest sweater. None of it counts as baggage and it is the single biggest saving available.
2. Compress what remains. Compression cubes genuinely work on fleeces and puffers, because those are mostly trapped air. They do nothing for shirts.
3. Layer instead of packing separately. Three thin layers are warmer than one thick one and pack far smaller. A merino base layer takes almost no space and does most of the work.

• Do not pack an outfit per day. It is the single most reliable way to double your clothing, because it stops you counting items.
• Do not use the expansion zip. On every airline in our size table, an expanded carry-on is over the limit - and Alaska says so explicitly.
• Do not pack liquids in the middle of the bag. They may need to come out, and they leak. Top of the bag, in a sealed pouch.
• Do not bring a third pair of shoes. They are the bulkiest and heaviest thing you can pack and you will wear two pairs.
• Do not save packing for the morning of the flight. Decanting toiletries at 6am in a departures hall is how people end up buying travel-size shampoo at airport prices.

1. Close the bag and measure it, including wheels. If it bulges, it measures larger than its empty dimensions and that is what a gate sizer sees.
2. Weigh it if you are flying internationally or on Frontier - see best luggage scales. A 7 kg cabin limit is easy to exceed without noticing.
3. Check the liquids bag closes properly. An overfilled quart bag that will not seal is a failed bag even if every container inside it is compliant.
4. Confirm your power bank is in the carry-on, not the checked bag. Spare lithium batteries are prohibited in the hold.
5. Put the tech pouch and liquids where you can reach them without opening the main compartment.