Body Glide or Blister Block...have found Body Glide at the large sporting goods stores, and have found Blister Block at
Walmart & Walgreens, in the first aid/bandaid department (it's made by Bandaid company) While you're in the bandaid dept, get a package of the blister bandaids...these work unbelievably well when you already have a blister. Every time we've taken people for the first trip, we've tried to get them to use Body Glide or Blister Block in advance...and heard, Oh I won't have problems, I"m used to walking in these shoes/sandals/flip flops. And they get a blister & the beginnings of more. So we hand out the blister bandaids for the existing blisters, and they slather the Blister Block on everywhere that's a "hot spot" for more blisters.
Way back in the day we tried powder...did nothing...we tried anti-perspirant...did nothing.