Herbalists the world over use mint, as a premier stomach tonic, to counteract nausea and vomiting, promote digestion, calm stomach muscle spasms, relieve flatulence, and ease hiccups. Menthol, the aromatic oil in peppermint, also relaxes the airways and fights bacteria and viruses. Menthol interferes with the sensation from pain receptors, thus it may be useful in reducing headache pain. Scientific evidence suggests that peppermint can kill many kinds of micro-organisms, and may boost mental alertness. In one study, people who inhaled menthol said they felt as if it relieved their nasal congestion, although it didn't increase their measurable air flow.
I carry peppermint oil and use a drop of it on the temples for headache relief.