I always keep a bottle of Litsea Essential Oil (£4.35 for 10ml) in the car, as I find it more effective than coffee in helping me stay alert behind the wheel. I put about four drops on a hankie and inhale from time to time. It can also be used in a burner, diluted in a massage oil or added to a warm bath.
Litsea essential oil is steam-distilled from the small, pepper-like fruits of a plant commonly called may chang, which grows wild from north-east India to south Vietnam. It is a non-toxic and non-irritant oil that is soothing and uplifting. It is used to treat stress-related tension, which may cause conditions such as headaches, high blood pressure, travel sickness, indigestion, flatulence and muscular aches. It has similarly been used to ease arrhythmias.
Source - Scotsman