mpointon, I use an excel sheet with the tracks I want to collaborate on and some keywords about the lyrical theme, what kind of feel/groove (country, r&b, smooth, gritty, etc.) and i also use a similar method as stella, recording brief snippets if i have a musical idea i don't want to forget. I used to think that if it was good enough i would just remember it in the future but I why not save the effort, if i'm in a position to jot it down or make a short sketch?
this way, i have a hard copy of my plans. i can't forget about them if they're right on the page! i can choose not to look, that's another story... it also gives me a list of things to experiment with, if one ideas not really happening on a given night I'll try something else... sometimes i'm not really jiving with any of the ideas that seemed so "great" earlier. then i get to look at why a certain idea didn't work, maybe i'm not in the right mindset, my voice is tired, oh, maybe the idea is meant for another song!...
hope that helped, typing this out surely reinforced it for me, at least ;)
Love and blessings to you on your path!