+1 on the Spenco Second skin. I don't have alot of experience treating blisters on the trail (happy feet all my life), but I put some of this stuff on a rubbed raw hot spot on my heel and then covered that with a knuckle bandage, and everything was gravy the rest of the day.

Knuckle bandages across the back of your heel - its my all purpose bandage for boo boos and up, it will prevent hot spots from becoming worse.