This pack is my go to pack for what youve described. Small when its empty, expands to a decent size if needed. Condor stuff isnt great, but I've put over 35lbs in there for extended periods with no sign of seams/straps coming loose. Voodoo makes a version of it as do half a dozen other companies (Maxpedition has a nice one IIRC). Can get it cheaper if you go for the Tan version instead of ATACs. Catch is it wont mount to your PC. IMO thats better however, as you can access your pack without removing your 2nd line kit.