It takes time to break habits and replace them with new ones, but it does happen.
http://eatthis.menshealth.com/home aka "Eat This Not That" is a fascinating website, full of useful and interesting info on what to eat and what NOT to eat.
If nothing else, get their daily email updates, and check them out. Some of the things you'll learn (such as what food companies do and the loopholes they exploit in their labeling) will strengthen your resolve to not let another ounce of the crap that gets passed off as food to ever enter your body again!
The things I look out for today is carbs, fat and sodium. I'm no expert, but being middle aged, to avoid learning about these things is to pretty much sign a death warrant.
You certainly don't have to go vegan. I'll never do that, and I do like to know what you can get away with, and just eat sensibly. I don't always adhere to it, but more often than not I do, and I can at least maintain weight and not gain any.
I have very few supplements, from flax seed oil (good for lowering bad LDL cholesterol), and some vitamins.
Exercise-wise.... Swimming is a great way to burn it off, but even just go for a walk....and working on the 'puter as much as I do, I make myself get up and go for a walk around the block, (did it 3 times last night) and a few minutes later I'm back and somewhat recharged..... but aside from that, walking is one of the best things you can do for yourself.
I have a home fitness machine thing, someone gave it to me, but it rarely gets used, by me or any of my friends that see it and want to use it.