I hate how hot and sweaty my back feels when I'm biking with a backpack. I don't do it if I can help it. I have an enormous rear basket, a grocery bag pannier, a kitty litter pannier, and a trailer with a huge plastic tub on it. I never have to wear a backpack on my bike anymore! I just bought a new and bigger rear basket, and gave my merely "big" basket to my daughter so she doesn't have to bike to school with her backpack on either.