Carry-On Only: A Packing System That Works

• Decide to do laundry. After that, a two-week trip and a four-day trip need the same bag.
• Pick two neutrals and one accent. Colour discipline is what makes a small number of items produce many outfits.
• Shoes are the real constraint — they are heavy and rigid. Two pairs maximum, one worn.
• Check the size and weight rules for every flight, not just the first. They vary enormously.
• Weight is usually the limit before volume is. Many airlines cap cabin bags at 7–10 kg.

The decision that does all the work

A four-day trip and a fourteen-day trip require the same clothes if you wash things once. That is the entire concept. Everything else is implementation.

Most people intuitively resist this, because laundry sounds like a chore imposed on a holiday. In practice it is: a sink, a squeeze of soap, ten minutes, and a night on a hanger. Or one visit to a launderette that costs less than a single checked-bag fee. Against that, you save the daily cost of dragging a large case up stairs, through stations and into taxis, plus the risk of losing it entirely.

Concretely, most trips need about four to five days of clothing, regardless of length. That is the target.

Fabric choice makes the difference between this working and not:

• Merino wool resists odour remarkably well and can be worn several times between washes. It is the single highest-leverage material change for one-bag travel. Lightweight merino t-shirts are expensive and earn it back quickly.
• Synthetic blends dry overnight, which is what makes sink-washing practical.
• Cotton is comfortable and the worst option here: it holds odour, absorbs water, and takes 24 hours or more to dry.

The capsule

The reason a small wardrobe usually fails is not quantity but coordination. Ten items that do not go together produce roughly ten outfits. Ten items that all go together produce dozens.

So impose a palette: two neutrals plus one accent. Navy, grey, and a colour you like. Every top must work with every bottom. If an item only works with one other thing, it does not come.

A typical week's capsule for temperate weather:

Category	Quantity	Notes
Tops	4–5	Mostly merino; mix short and long sleeve
Bottoms	2	One neutral trouser, one jeans or chino
Layer	1	Merino jumper or light fleece
Outer	1	Packable waterproof shell
Underwear / socks	4 sets	Quick-dry; wash mid-trip
Sleepwear	1	Can double as loungewear
Shoes	2	One worn, one packed
Occasion item	0–1	Only if the trip actually requires it

Then apply two filters ruthlessly.

The "just in case" test. Anything packed for a scenario that has not happened yet — the possible hike, the possible nice dinner — stays home unless the scenario is on the itinerary. Buy it there in the unlikely event you need it. Just-in-case items are the single largest source of dead weight in a bag, because they are never worn and always carried.

The wear-twice rule. If an item will not be worn at least twice, it needs a compelling reason to earn its space.

Shoes are the real constraint. They are heavy, rigid and hard to compress, and each pair displaces a large fraction of a carry-on. Two pairs is the ceiling: one versatile pair worn on the plane (the heaviest ones, always), one packed. A third pair is almost never justified.

Bag, size, and the rules that vary

Carry-on allowances are not standardised, and this is where confident packers still come unstuck.

Many US carriers permit around 22 × 14 × 9 inches (56 × 36 × 23 cm) including wheels and handles. IATA has proposed 55 × 35 × 20 cm. But several European low-cost carriers allow a much smaller free bag — figures around 40 × 20 × 25 cm are common — and charge for anything larger.

Two rules that save real money:

Check every flight on the itinerary. A bag that flies free on your transatlantic leg may not on the regional connection, and codeshare flights follow the operating carrier's rules, not the one that sold you the ticket.

Watch the weight limit, not just the dimensions. Many airlines outside the US cap cabin bags at 7–10 kg, and it is enforced at the gate more often than people expect. Since the limit covers bag plus contents, a heavy hardshell case can eat 3–4 kg of allowance before you pack anything. For weight-limited routes, a soft bag is meaningfully better.

Beyond that, a few features genuinely matter: a clamshell opening (packs and unpacks like a suitcase rather than a rucksack), an external pocket for liquids and electronics so security is not a full unpack, and straps you can stow if you need to hand the bag over at a gate.

Packing method

Compression, not cleverness. Packing cubes do not create space by themselves; compression cubes do, by expelling air from soft items. Their real value is organisational — you can find things without excavating, and repacking each morning takes seconds.

Roll soft, fold structured. Roll t-shirts, jeans and knitwear; it saves space and avoids hard creases. Fold shirts and anything tailored, ideally with a garment folder. Do not agonise over this — technique is a rounding error next to how many items you brought.

Fill the dead space. Socks and underwear go inside shoes. Shoes go sole-to-sole in a bag at the bottom, near the wheels.

Heavy at the wheels. Weight low and against the back panel keeps a wheeled bag stable and a backpack comfortable.

Liquids: pack to the 100 ml rule. Containers of 100 ml / 3.4 oz or less, in one transparent resealable bag of about a litre. Some airports with newer CT scanners have relaxed this, but the rollout is patchy and restrictions have been reinstated at short notice, so assume the strict rule unless you have confirmed otherwise for every airport in the itinerary.

The larger win is eliminating liquids entirely: solid shampoo and conditioner bars, solid deodorant, a toothpaste tablet, a bar of soap. None of it counts toward the bag, and none of it can leak over your clothes at altitude.

Electronics: one charger, minimal cables. A single multi-port GaN charger replaces three bricks and one cable per connector type. Spare lithium batteries and power banks must travel in the cabin — most airlines prohibit them in the hold on fire-safety grounds, which is another quiet argument for carry-on only.

What actually goes wrong

Souvenirs and shopping. The bag that fits perfectly on the way out has no slack for the return. Leave roughly 10–15% free, or carry a packable tote for the flight home.

Gate-checking. On full flights, cabin bags get taken at the gate. If yours might, keep medication, documents, electronics and a change of clothes in a small personal item you keep with you.

Weather changes. The response is layers, not more clothes. A merino base, a mid layer and a packable shell cover a wide temperature range in three items.

Formal requirements. A wedding or a business meeting genuinely may need something that does not compress. Be honest about it — the system flexes, and one garment bag is not a failure. What it should not do is quietly become "and also these other four options."

Trips with real gear. Diving, climbing, skiing, photography with long lenses. Carry-on only is a wardrobe strategy, and it does not survive contact with equipment. That is fine; use it on the trips where it fits.

Why it is worth it

The clothes are the smaller part of the payoff. What you actually get is: no bag drop queue, no baggage carousel, no lost luggage, no checked-bag fee, and the ability to walk straight out of an airport onto a train. On a multi-city trip that compounds into hours saved and a noticeably lower background level of hassle.

The trade is that you wear the same five things repeatedly and wash them once. After one trip, almost nobody considers that a cost.

Further reading: The TSA publishes the current US rules on liquids and prohibited items, and the IATA guidance on lithium batteries covers what may and may not travel in the hold. Airline cabin allowances change frequently — always check the operating carrier's own page for each leg.