Salicylic acid. It's one of the topical applications used for acne treatment, and it just so happens to be a natural part of aspirin.
Crush up the pill and add some water to make a paste. Apply the aspirin paste to your pimple and wait for several minutes. Rinse off without rubbing too much, and the pimple should diminish in redness and size. Spot treatment for those "haven't showered since Friday" weekend camping trips where you want to look your best.
Possibly true fact: the taste of salicylic acid can discourage bears from gnawing on your face.