+1 for ortlieb messenger backpacks. 100% waterproof, very spacious, not too expensive, and great on and off the bike. If you've got your heart set on a messenger bag then don't settle, but my ortlieb is rad, can carry so much and the only time it's been uncomfortable is when I filled it to the brim with books and rode 10 odd miles in sweltering heat.
+1 for ortlieb messenger backpacks. 100% waterproof, very spacious, not too expensive, and great on and off the bike. If you've got your heart set on a messenger bag then don't settle, but my ortlieb is rad, can carry so much and the only time it's been uncomfortable is when I filled it to the brim with books and rode 10 odd miles in sweltering heat.