As a military trucker, I know all sorts of different ways. Heres some of the methods I used overseas.
(In +52'c heat too!)
Open a window. Fresh air will help you out.
Coffee. Mixed blessing. Caffiene makes you feel awake, but the nice warm guts make you feel comfy and drowsy.
Red bull. It does work, but its like your body gets used to it way to fast. Then you start drinking 5-9 cans per day.
Poke yourself in the leg with a pen.
Call someone. Or talk to passengers. The conversation reactivates the brain.
Drink cold water. Good for you and surprisingly refreshing.
Have a conversation with yourself. Pick a topic and explain it to yourself in great detail.
CB or HAM radio. Always worked for me. Always somebody to talk to.
Dance. Wiggle your feet and hands, keep the blood circulating.
Failing that. Sleep. One sleep cycle (45mins to an hour.) Make sure you find a safe place to do so. Truckstop, desingated roadside turn out, etc..