Here's my list:

Modafinil: -10 all the mental energy loss of sleep deprivation without feeling sleepy, worst thing I ever tried

Resolutions: +1 I promise myself to do X regularly; then due to external circumstances I cannot for a few days and resolution dies even when external circumstances cease

Utility Function Experiment: +2

Messing with Internet via /etc/hosts hacks etc.: +2 unfortunately my work requires me being on Internet all the time, might work better for people who don't have this

Regular physical exercise: +4 - time and energy lost on it seem to be more than balanced by increased productivity for the next few days after

GTD 2 minute rule / execute by default: +6

GTD getting things off my mind / making lists of everything / reviewing them regularity etc.: +6

In both cases not by high efficiency of doing that, but by how my productivity collapses when I don't do that. My baseline productivity seems very low without GTD.