If I were just starting out and if you gave me $20 tomorrow morning I would post a load of auctions on eBay. Then in a few days my investment would come good plus a whole lot extra. I would get rid of a lot of junk first and then use that money to buy advertising for new products.
Honestly? I'd probably but $20 worth of coffee or energy drinks and then bang my head on the desk wishing I would have invested it in some kind of advertising.