I've mentioned Eugenia Bone's post on "kitchen ecosystems" before; it is an excellent article.
I was really excited when I read her post, because it sums up so many of the things that make cooking from scratch much easier and simpler. There's an ebb and flow to what you're doing, and you need to be fairly nimble and flexible, but beyond that you need to find specific things that work for you. There are a lot of pantry "must-have" lists out there, and for a long time (especially when I wasn't cooking without recipes but wanted to start) I tried to follow their guidelines.
After spending a lot of time cooking - much of it from scratch, often without a real recipe - I've decided that those lists have it exactly backwards. The writer's "go-to" kitchen staples probably aren't yours, and even if they might some day be things you'd use, they're not worth stocking if you don't know what to do with them right now.
I think it makes a lot more sense to cook a lot and get a feel for the types of things you use on a regular basis. When you can think of one or two things like that, by all means stock up!
Or better yet, focus on playing with those ingredients: maybe you do a lot of cooking with beans. You could buy a lot of canned beans when you see them on sale, or you could buy some dried ones and cook up a big batch one weekend. Divide them into "can-sized" portions, if that's how most of the recipes you currently use are written (1 2/3 C cooked beans (from scratch) = 1 can beans), and freeze. Maybe get those beans from your local farmer's market ("fresh" dried beans are really worth the effort to find, if that's possible for you), or maybe you buy some cheap ones from the supermarket. Either way, do that a few times with different beans and you have the backbone of your cooking - and you'll be well on your way to a vibrant kitchen ecosystem of your own.