Shoppinglist, what will i take with me?

Knowing myself i usually pack too much (better save than sorry). Therefore i didn't want to buy a backpack too big. I ended up choosing a Haglöfs OXO 550Q meaning 55 litres contents.
There are some things i really want to take with me, first of all my canon 350D with 2 lenses, a tripod for my camera, my laptop and my trumpet (i've been playing the trumpet since i'm 8-9 years old).
Fortunately i found a small backpack from Lowepro, where i can stash both my laptop and SLR camera (including lenses) in special compartments. this means i don't have to take my a seperate camerabag with.