Start with a realistic load
First decide whether the backpack will be your only luggage or an addition to a suitcase. The same weekend can require very different features depending on that choice. Clothes and shoes need volume, while a laptop needs a suitable compartment and changes how the weight is distributed. Use a comparable load for a fitting instead of putting an empty bag on your shoulders and assuming it will feel the same later.
A capacity stated in litres does not describe a standard interior shape. A narrow main compartment may suit a long packing cube, while a wide opening makes several smaller pouches easier to reach. Check whether heavier objects can remain close to your back and whether you can access the compartment you need when everything else is fully packed.
Check back length and straps
On a model with an adjustable carrying system, the correct torso setting is an important starting point. Your overall height alone does not reliably identify it. Follow the particular manufacturer's fitting instructions or arrange a fitting with assistance. Do not keep tightening the shoulder straps to force an unsuitable backpack to sit still.
Walk with the loaded model for several minutes, turn around and sit briefly. Straps should not rub against your neck, and your arms should move freely. A chest strap helps stabilise the position but should not feel restrictive. If the pack has a load-bearing hip belt, check its position according to its instructions. A simple narrow waist strap does not necessarily perform the same role.
Take the backpack off and put it on several times. You will do this more often during a travel day than during a quick shop fitting. Are the handles easy to reach? Do loose strap ends catch on things? Can you hold the bag in front of you in a narrow aisle without protruding parts striking other people? These small movements can expose problems that standing in front of a mirror misses.
Decide after a trial packing
Carry the packed bag over a route similar to your walk to the station. If the load becomes uncomfortable, first reconsider what you have packed. A different carrying system cannot compensate for every overloaded packing list. Note which pockets you actually use, and avoid extra organisational features that merely add material and empty weight.
For flights, the fully packed dimensions and your booked baggage category still matter. A compressible backpack only helps when its actual contents allow it to compress. Keep the product dimensions in your notes, but check the operating airline's conditions for the particular booking again. The right weekend backpack is the one that works with your belongings, body and route together.
