Stack Exchange is meritocratic. Users get a few powers at first, then more if they show that they are knowledgeable.
The engine was created this way to control quality. It was always meant to be a site for people who knew what they were talking about - experts or enthusiast amateurs.
I believe your concern is that, as a casual user, you believe you will never get the required points and privileges to make yourself useful (unable to comment, unable to answer "protected" questions, etc).
It has already been pointed out in comments that you can earn some rep by making edits. If you do this, please make sure they are good edits.
The fastest way to get points, though, is to answer questions. Do not underestimate yourself! There is bound to be something on the network that you can answer! Maybe it's on Anime & Manga, maybe it's on Electronics, maybe it's on Seasoned Advice.... but it's there.
Alternatively, you can ask questions. If you can post a well-researched question on a popular subject, you can also build up reputation. Something you wondered about in your favorite TV show? Try Movies & TV. Something you need solved in a video game? Try Arqade. There's bound to be something that interests you, that hasn't been asked yet.
So why would you ask or answer questions about, for example, cooking... if you want to comment on Super User? Because if you get 200 points on any Stack Exchange site, you will get a +100 bonus on the other sites - relieving most of the restrictions.
I admit that this means you'd have to be a little more than a casual user, at least for a short while. But you can do this - and have some fun in the process too. Keep track of the subjects that already interest you, and at some point, something's going to turn up that you can answer.