I have a Messenger style diaper bag, and for me, after about 6 days of theme parking it, my back was DONE. I could take NO more. Of course, I am incredibly out of shape, and the hotel bed was as hard as sleeping on the floor. Not to mention all the snacks, diapers, wipes, juices, sippys, toys, extra clothes,and nookies I had to carry around, That didnt help matters much. But I could switch sides with it and It was nice that it wasnt on my back. I always get freaked out with backpacks, Im always afraid that someone will try to break into it, steal my wallet or something.