Looks like 55L is the average! I was just wondering if most people go for 55L then a 10L detachable day pack thing (If you know what im talking about) so in all it would come to 65L?
Basically im pretty week and dont want to take too much.
Do they do packs with wheels??
The packs with wheels are by eaglecreek.
You are looking at the switchback and crossroads models. Be warned that these packs are very expensive. They'll cost you three times as much as a normal backpack and unlike others don't come in women's fits.
There are also some travelpacks by Jack Wolfskin and other companies, but all those I have seen aren't worth their money. They are too large (80 l and over) and their strap system is laughable and more decoration than anything.
As usual, try your backpack on before you buy it. Go to a store and compare the eaglecreek carrying system with a regular backpack from deuter or another good company and then decide. A good store will let you pack something heavy into the bag so that you can get a real feel for it. A 55l pack will weigh something in the neighborhood of 20 kgs when 2/3 full.