How to pack three nights into a cabin bag

Cabin-only sounds like one standard and it is four, and the differences are large enough to change what you take.

Ryanair's overhead trolley is 55 x 40 x 20 cm at 10 kg, and it cannot be bought on its own: it comes inside Priority and 2 Cabin Bags. Wizz Air's is 55 x 40 x 23 cm at 10 kg, sold inside WIZZ Priority. Bulgaria Air gives you 55 x 40 x 23 cm at 10 kg on every Economy fare, including its cheapest. Lufthansa, Austrian and SWISS all give you 55 x 40 x 23 cm at 8 kg from Economy Light upward.

Under all of those sits the free under-seat bag, which is 40 x 30 x 20 cm on both low-cost carriers and 40 x 30 x 15 cm on the network ones.

So before packing, answer two questions: which carrier, and which bag on that carrier. Everything below follows from the answer.

The binding limit moves from airline to airline, so the same packed bag can be fine on three of them and over on the fourth.

On Ryanair the trolley carries a 10 kg limit, and the free under-seat bag carries no published weight limit at all and is not weighed. There, size is the whole test.

On Wizz Air both bags are capped at 10 kg, which is generous enough that size usually binds first.

On Lufthansa, Austrian and SWISS the trolley is 8 kg. That is 2 kg less than the low-cost carriers, and it is the number most likely to catch someone who packs boots and a laptop into a bag that fits perfectly.

Bulgaria Air caps differently again: the cabin bag and the personal item together may not exceed 12 kg in Economy, so a 10 kg trolley leaves 2 kg for everything beside it.

Write your number down before you start.

Count wears rather than days, then cut anything that serves only one of them.

Three nights is usually four days of clothes once you count both travel days. Two bottoms, three tops and one warm layer covers it, with the fourth day repeating whatever is cleanest. One pair of shoes, on your feet.

The test for every other item is whether it works with at least two of the things already in the bag. A shirt that goes with one pair of trousers is a passenger. A second pair of shoes for one dinner is the single most expensive item you can pack, because shoes neither compress nor stack.

This is also where the weight goes. Clothes are rarely what breaks an 8 kg limit. Shoes, a hard-shell case, a laptop and a full toiletry bag are, and three of those four are avoidable.

Anything on your body is outside the allowance, on every airline here, and a winter trip turns that into several kilos.

Wear the coat, the jumper and the heaviest shoes to the airport. On a three-night trip in January that decision alone is the difference between a bag that closes and one that needs a purchase.

Wizz Air also publishes a short list of things carried free on top of the bag: a coat or a blanket, your phone, reading material for the flight, and anything bought airside after security. Infants add food for the flight and a foldable stroller or small crib, and one pushchair per child is checked free.

A neck pillow is not on that list. Wizz Air says so directly, and it has to go inside the bag, where it is one of the worst volume-to-value items you can carry.

Take the pillow only if you would still take it at the cost of a jumper.

A cabin bag is measured by its widest point, not its average, so the goal is flat faces rather than a clever interior.

Put the flattest items, a laptop or a folder, against the 55 x 40 face so they brace the bag instead of letting it bow. Roll soft clothes and lay them along that face. Put shoes at the hinge end, soles outward, and fill them with socks and chargers.

Leave the front pocket empty. Wizz Air's conditions of carriage state that the published dimensions include side pockets, so a loaded outer pocket is measured as part of the bag.

A soft bag is better than a hard shell for exactly this reason. Ryanair's sizer is a rigid frame and the bag is expected to drop in unaided, which a soft bag will do with a squeeze and a hard shell will not.

Compression cubes help with volume. They do nothing for the 8 kg limit.

Your cabin bag can end up in the hold without you agreeing to it, and this is the rule that protects you from that.

Wizz Air's conditions of carriage let it carry even a fully compliant trolley in the hold, free of charge, for operational or safety reasons. Ryanair's gate process is the same in effect: a bag that is refused is left at the aircraft steps or in the gate bag trolley.

So medicines, keys, passports, chargers, anything valuable and one change of clothes belong in the personal item, which stays with you. On Ryanair's Priority product and on the network carriers, that second piece exists precisely because you have it.

This is not a rare scenario on a full evening flight from Sofia. Lockers fill, and the last few trolleys go below.

Pack the small bag as though the big one might travel separately, and the worst case becomes an inconvenience rather than a problem.

More cabin-only plans collapse in the bathroom than in the wardrobe, because full-size bottles are heavy and awkward at once.

Decant what you need for four days rather than carrying what you own. Two people travelling together need one set of toothpaste, shampoo and sun cream between them, not two. And anything bulky and cheap, sun cream especially, is easier bought at the destination than carried to it.

Security rules on liquids are set at the airport rather than by the airline, so check the departure airport's own page for the rules that will apply to your tray.

One small upside applies on Wizz Air: anything bought airside after security travels free on top of the allowance, so a bottle picked up past the checkpoint does not count against your bag.

Keep the pouch at the top of the bag. Being made to dig for it in a security queue is how a well-packed bag becomes a badly packed one.

Cabin-only is a saving when the bag is free. When the bag is bought, it is a preference, and it is worth knowing which one you are exercising.

On Ryanair the trolley costs €12.49 to €36 at booking and a 10 kg hold bag costs €10.49 to €44.99 for the same size of case. The bands overlap, so the hold bag can be the cheaper purchase, and it removes the gate sizer from the day entirely.

For two people on a three-night winter trip the sums often favour the hold. One shared 20 kg bag is €21.49 to €59.99 at booking, against two trolleys at €12.49 to €36 each, and Ryanair lets passengers on the same booking split their combined weight as they like up to 32 kg a bag.

On Bulgaria Air and the Lufthansa Group carriers none of this applies, because the trolley is in the fare from Economy Light upward. The exception is the Lufthansa Group's Economy Basic, sold on some routes below Light, which leaves you the personal item alone.

Do both checks on the bag you are taking, in the state you are taking it, and the rest of the trip takes care of itself.

Measure the widest point of each face, including any pocket now sticking out. Then weigh it, if the carrier publishes a number: 10 kg on the Wizz Air and Ryanair trolleys, 8 kg on Lufthansa, Austrian and SWISS, and 12 kg for the cabin bag and personal item combined on Bulgaria Air. Ryanair does not weigh its free under-seat bag.

If a face is over, move the offending item to the centre rather than trusting the fabric to give at the gate.

The cost of skipping this is fixed and public: €70 to €75 at a Ryanair gate for an oversize cabin bag, €55 to €65 at a Wizz Air one, per bag and per one-way flight.

Two minutes at home, against one of those, is the best rate of return in travel.