Thought I'd chime in that after many years of using all the different packaged milks (various soy milks, rice milks, nut milks, hemp milk, etc), I have recently started making my own nut and seed milks and find them easier, lighter on the environment (not constantly going through containers), pretty inexpensive in the end, and so fresh and delicious! Not watery and boxed-tasting like some of the commercial nut milks (although in general I do like the taste of many of the boxed options).
My method is a little different than the one cranberryavo mentioned, but very similar. I soak a full cup of nuts/seeds in water (almonds are a mild and rich tasting first one to try) overnight or all day, then rinse them very well and blend them up in the blender on high with about 4 cups of water. After straining out the pulp (with a strainer, or cheesecloth or something similar), I'll sometimes mix in a pinch of salt, perhaps some agave (or blend up the liquid with a date or two), perhaps some cinnamon, or whatever I feel like-- then put the milk into a large jar in the fridge. So easy, and I use the pulp for crackers, cookies, as an ingredient to mix with cut fruit for a 'cereal' or to make a nut cheese type of recipe.
I felt kind of silly the first few times I made it because I've been meaning to for years and always thought that somehow it would take a lot of time or effort. But it's so easy and quick! I've never had a batch go bad, but I always use it up within, say, 4 or 5 days at the most. And it tastes to fresh, that's the best part I think!