A wire strainer.
A third of a cup of dried nuts, seeds, or grain. (For instance, flax seeds, pumpkin seeds, or oats.)
A tablespoon of water.
Flavoring. (Recently I've been using maple syrup, vanilla, and a bit of salt. Yum!)
So, you combine these ingredients in your blender on a high setting. You only put in a little bit of water in at first because you want the seeds or nuts to get ground up. You run the blender, push the nuts back down, run the blender, push the nuts back down... okay, now you have a pasty mix. Add some more water (a cup or two) and stir. Now you're going to pour your wet, pasty mix through the strainer. What comes out the other side should be a cloudy liquid suitable for your granola or whatever.
The great thing about this is that you can put the solids in tupperware and put them back in the fridge. Just grind them up more, add some more water, and repeat.