Well, it's little thing, but I like to add these as globals:
TRUE = 1
FALSE = 0
NULL_ID = -1
Sometimes I use 0 and 1 instead, but I like these for conditions like:
PlayerActive = TRUE
or, more usefully, calling a function, where I want to make it clear I'm passing a boolean val:
Func SetFoobar(TRUE, 100, 200, 180)