Okay, so I was hiking in my sandals today because I have a busted toe. This isn't as bad as it sounds, Chacos have a Vibram (i.e. very sticky) lugged sole and are made for hiking, and they worked pretty well (note that I have the older heavy-duty Chacos, not the wimpy new ones). Unfortunately there was one place on the strap on both feet that started rubbing a hole in my skin. So I duct-taped my skin, then duct-taped the strap. Problem solved.
I was doing a fair amount of uphill and downhill action, and managed to get a blister on one of my toes too. And the blister burst. Ouch! So I cleaned it as best as I could on the trail (used a baby wipe from my daypack, intended for, err, nether end use, but just as good for any other cleansing task), and then... well. You guessed it. Duct-taped that sucker. Problem (mostly) solved.
Duct tape. Good for more than ducks. :-).
Now, you might wonder, what was I doing wearing sandals without socks? Because surely socks would have padded against the straps at least, right? Well, the problem is that socks allow my feet to slip around inside the sandals too much. So I end up with blisters on all my toes because they're sliding back and forth, and blisters on the arches of my feet because they're sliding up and down the arch support. Sad to say, my feet blister if you sneeze at them, the closest I've gone without a blister was last week when I was wearing the trail runners, and even there I had sore toes at the end. So I'll just continue to be a duct tape messiah and now that I know where the sandal straps rub, I can pre-duct-tape them there and be done with it.
-- Badtux the Hiking Penguin