99% of the time, my starting point is a sketch or a new item I just purchased. If I want to use new stamps, I'll go through my stash of patterned papers to find something that would be a great match and then I find a sketch that will work with those elements. If I want to play with a sketch, then I'll go through my stamps and find something that is the right size to work with it.
Now that I think of it, stamps, papers and sketches always seem to be the first steps involved in creating. I guess those are the items I couldn't live without!