I think my tip would only be useful for people who like to knit or crochet, but here goes: don’t buy yarn from the store, get a cheap, gently-worn sweater from Goodwill or similar (make sure the whole thing is hand-seamed and not serged or you’ll get into trouble!) and unravel it. You’ll get tons more yarns for your money!
[Kacie posted this tip to the Readers’ Tips box. It originally appeared as a comment in The Complete Tightwad Gazette giveaway.]