To add to what Darvin said, if you know the dungeon will cause Weakening or Corrosion then you can use bring the appropriate potion as a preparation.
Also, my preferred shop preparation is the one that provides Extra Potions. This usually means that if you end up needing a potion during the run, you can use one of the three potion shops to buy one.
Finally, if you're about to drink a Burn Salve potion, you should seriously consider desecrating Earthmother's altar. He punishment is 5 corrosion, so you'll end up with 30 piety and 3 indulgences for "free".