We didn't care for the Body Glide because we found it to be too sticky. I pack a can of spray deodorant. Spraying it on your feet really helps to avoid blisters.
If you have different shoes/sandals to wear in the evening, it will give your daytime shoes a chance to air out.
Carry as little as possible. I take the smallest purse possible, just big enough for tickets, band-aids and a small sunscreen. Nothing is worse than lugging a back pack when it's a hundred degrees outside. Take advantage of indoor shows and attractions at reasonable intervals to cool off.
The first person I've seen on the DIS who also thinks Body Glide is too sticky! I bought it for our first trip and put it on with my Crocs flip flops. It was so sticky that I didn't even make it to the bus stop before I had to wipe it off with a wet wipe. I was miserable at the parks with the stickyness and couldn't wait to get back to the room to change into socks/sneakers.

I usually swap out my shoes in the afternoon. Rotating also helps to avoid blisters.
We use a backpack, but it's a hydration backpack that we fill with ice at the resort in the morning and then refill with free ice water in the parks throughout the day. DH likes that it keeps his back much cooler than a regular backpack and it's handy to give the kids a little drink throughout the day.
As for all the chafing comments/suggestions, I would recommend anti-chafing gel. (Monistat and Lanacane both make one) It dries to a powder soft feel but would avoid any powder meets water issues
