[QUOTE=fatbat]I find the single strap messenger bags are the best compromise for carrying a little vs carrying a lot. Just removed something big from the bag? cinch up the main strap, and you're good to go.
Backpacks tended to not be stable on my back, flop around, and interfered with head-checks. /QUOTE]
This is what brought me to buy a mes bag. I dont always carry alot on my commute and when I do the bag handles it. I can take something out while riding and cinch the pack up as I go. Back packs have a place also and I plan on investing in one.