Yeah, boxed cereal is a total ripoff. It's good to have around during exam weeks, though -- beats fast food. Oatmeal, otoh, is the best. Cheap, easy to microwave and good for you. Don't waste your time on those stupid seasoned individually packaged oatmeal, though.
My cheap food excitement is that I'm getting a pressure cooker for my birthday! Now it'll be super easy to use dried beans, which are also ridiculously cheap yet good for you.
I'd pass on the canned veggies because of the sodium content, but frozen veggies aren't a bad deal. If you buy in season, you can also get pretty good deals on fresh veggies. Speaking of that, another good health food/cheap investment is a salad spinner. Those bags of salad cost over 2 times as much as a head of lettuce.