I've used both backpacks (on the smallish side) and fanny packs. I've found, that for me, the backpack straps start chaffing after 3-4 days in the heat. And I have taken it off and almost left a restaurant without it. But my fanny pack has never been left behind. I don't carry water with me very often. If we do then dh uses the backpack. My only issue with the fanny pack was that my lower back would start to ache. A CM at TL told me to 'turn it around, the way it's meant to be worn'. Ahhh, dopey me. Felt much better if I let it sit on my fanny. Then I felt like it was open to theft but as dh said, 'your backpack was behind you also'. Keep it zipped and you'll be fine. But again, I don't carry too much stuff....passes (for everyone), chap stick, digital camera, little cash and a poncho (disposable one).