Keep a spray bottle full of water. Set up a reminder to make you spray yourself with the water every 30 minutes. This might boost alertness through the mammalian diving reflex. I have halfheartedly tried this, and it definitely does temporarily boost alertness, but I don't know how long the effect lasts or whether tolerance develops. I'm slightly concerned that it could damage electronics.
Results were interpreted to indicate that the diving reflex is actuated by both facial cooling and apnea, but not by any direct effect of water contact other than cooling.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.