Caffeine really works for lessening water-retention induced puffiness under the eyes. Garnier makes a roll-on product based on this principle.
You can make your own product at home for less money, and have a higher concentration of the active ingredient (caffeine) if you wish.
I used a few tablespoons of aloe vera, combined with a teaspoon of caffeine in powder form (bought off e-bay) and put it in a jar. It works very well for my under eye puffiness which is due to water retention.
If you don't want to buy powdered caffeine, I would imagine tea bags containing caffeine or maybe even freshly ground coffee beans might work.