It occurs to me that I could use this with a different context for each store I frequent. For example, I like to get most dry goods items from Trader Joe's (where they're super-cheap) and produce at Whole Foods (where the quality is much better). I could use your system of organizing the list by area of the store and set contexts for each store -- e.g. "Trader Joe's" and "Whole Foods". I process the list before leaving the house (as you suggested), and when I'm in the actual store, OF shows me only the items I want to buy at each one.
This will be even more impressive once OF for iPhone comes out and it will already "know" which store I'm in. Eerie.