By your post I'm assuming you have the basics for riding a bike (safety / tools / repair kit). If not, you need to make sure you have them first and foremost. I'd say you're on the right track of what else you should get if you're getting into long rides, though you really should look at getting clipless pedals and shoes, bibs (and chamois cream), and a jersey all at the same time. A single, high-quality, jersey and bib shorts will last thousands of kilometres, and hang dry really fast between rides and washes.
-clipless pedals and shoes
-you will see a significant improvement in efficiency, meaning you can do longer rides and have more fun!
-mountain SPD might be the way to go as a commuter if you want to wear shoes that also have a tread and are decent to walk around in
-bib shorts
-great comfort improvement over regular bike shorts
-keeps everything snug and doesn't shift at all
-jersey
-made to be worn in the bent-over position of riding a bike
-snug, wont flap around
-has a zipper for hot rides
-has pockets that will eliminate the need for a saddle bag
-chamois cream
-will keep you cool and eliminate friction
-lower the chance of getting saddle sores
If you are maxing out your long rides at a couple hours, you can fit your food and repair kit in the jersey without a problem. Gatorade (with carbs) in one bottle, and a banana in the pocket is sufficient to fuel the ride. If you're going longer than that, then a saddle bag is handy for holding bulky repair items that will free up space for fuel in your pockets. Lezyne makes a great little saddle bag to store and keep your repair kit organized.