ebay bucks. Make sure you're enrolled in the program. You get 2% back on every purchase. Every so often, like today and tomorrow, they run promotions where they give you 5x bucks back, or 10%. Next thing is to buy as many household goods as is practical through
ebay on those bonus days. Things that are light but with a fairly significant cost are good, like razor blades, vitamins, and postage (yes, postage) are ideal because 1) they're usually cheaper on
ebay to begin with and 2) shipping costs are minimal. You don't get
ebay bucks on shipping costs, so buy the ones with the lowest shipping. All this of course assumes that you're still saving money over a different source - it would make no sense to pay 50% more to get 10% back.
Anyway, long story short, I've ended up with some really nice stamps I probably wouldn't have gotten otherwise, and I got them free or at a ridiculously low out of pocket cost. I now keep my watch list full of everyday items and buy them on those 10% days. And if you pay with Bill Me Later, you get an additional 1% for a total of 11% back. They're good days to stock up on postage if nothing else. It's like getting discount postage right from the USPS.