As a bike commuter I wore a backpack to carry my work clothes and such. I was riding 22 to 30 miles per day over those years. And on a few tours I rode with a Camelback. But after riding through a very hot Central America with that thing on my back, I gave it up and now let the bike carry all the weight. Riding with anything at all on my back now feels too constraining, hot, and tiring on neck and back muscles.