Do you have access to any sort of medication? Any of the OTC pain killers should be able to take care of a mild headache: Ibuprofen, Aspirin, Tylenol, Aleve, etc.

For non-med remedies, I sometimes find that massaging my temples helps alleviate mild headaches. Also, try not to keep your muscles tensed. Crack your neck. Just relax.

Edit - make sure you are well-hydrated, too.