To be something more tangible than just writing a check or making a paypal donation. Also it should be as easy a buying groceries.
I ended ud with these three cans, just as easy to buy as a carton of milk
When you buy the one in the left you safe on square kilometer of rainforest, and inside is a little certificate and coordinates to where your donation has been used
The one in the middle removes one land mine, and inside is a certificate showing you exactly where your donation is being used.
The one on the right gives 1ton of fresh water to someone who needs it.Inside, is again a certificate that shows where this particular donation is being used.