talking to myself.
also arguing with myself or an invented character to better understand my position in arguments
also fiddling with things. its not so much of an extremely necessary compulsion as much as it is something to help occupy my mind, because the way my brain works, i'm often thinking of something, following every free associative path, and have a soundtrack all at the same time. The fiddling cuts out the free association, which allows me to not be distracted. EDIT: thinking about it, doesn't need to be my fingers. pacing, placing books back on shelves at my work, drawing in the air, writing notes (even if nonsense) in my notebook that i keep in my breast pocket at all times, all help.
also planning for any circumstance, such as someone catching me in a lie (not that i do very much, but when i do i spend much of my free time planning around every response and covering every base)
EDIT TWO: And the fact that my current goal is to be crazy prepared [http://tvtropes.org/pmwiki/pmwiki.php/Main/CrazyPrepared]. i currently keep on my person at all times a: Mechanical pencil, ipod touch, flash drive with various files that i like to keep around, a different flash drive with a diagnostic tool, a debugging tool, and an operating system, a wallet (with the obvious), a small spool of string (weak enough to be cut with teeth, but strong enough to still be useful), a multi-tool, lip balm (i have chronic chapped lips), and finally a small 80 sheet notebook full of illegible handwriting, ramblings of things that don't exist, diagrams of things that don't exist, random strings of characters, maps of areas and planets that don't exist, entire pages that have been scribbled out, (poor) attempts at drawing, and so on.
and plugging TVTropes [http://tvtropes.org/pmwiki/pmwiki.php/Main/HomePage] when ever I think it relevent.