I think I may have mentioned my file titled "Cool Things To Use Sometime" before. Brandon Sanderson referenced his own Word document with the same name either on Writing Excuses or in one of his lectures (perhaps both). As evident by its title, I use it to hold writing ideas that I want to use sometime.
Any time I get an idea that isn't large enough for a full story, I throw it in "Cool Things To Use Sometime". My list is broken down into the three components of prose: plot, setting, and character. Right now, each has eight or nine ideas of varying complexity. Some are almost big enough to hold a story, others are only cool tidbits.
I recommend keeping a similar reference to any writer. Too often I'll try to write a story the moment inspiration strikes, but it almost always falls flat. If I write it down and let my emotions fade first things typically get better. They don't even need to be particularly good ideas. Anything that strikes you as "cool" in the slightest is appropriate to include. Consider it another tool in your toolbox.