Assault Backpack "Bober-M" 25L
Bober-M - one of the most popular and balanced backpacks. It's created by SSO company in end of 90-x years, and now modified. Now it's have Molle straps on sides and even weapon case.
Assault backpack - compact backpack, that usually used by Special Forces during local operations, when they don't need to keep everything. Only most necessary stuff. Good choice for 1-2 days Milsim or just Airsoft Games.
Another good feature of this backpack, that it have weapon case. You can put your gun (it fits almost all weapon models), on backpack and that's helps.
Smaller, than Adler on 10 Litres.