If it's a reduced match of 300yds or less, you'll be fine with your rifle. Grab some 55gr white box stuff from walmart (or heck even Wolf for that matter) and go shoot. Everything else is secondary to trigger time. 99.9999999%+ of people who start out can't hold and shoot at what their rifle is capable of. You don't need the latest greatest space gun to go out and have fun. If it's something you end up enjoying, then you can start to invest in it.
For your first match, bring your AR, and about 150 rounds of ammo. That's enough to shoot the course w/ sighters, as well as refine your zero if need be. A GI websling, though any two point sling will work. 4 20 round mags if you've got them, else 2 20 rounders if you can. 30's are legal, they are just a pain since you can't use them as a monopod and have to stay higher off the ground. A heavy work coat like a Carhart jacket or the like, and a work glove for your support hand. A piece of camp pad or carpet scrap for shooting mat, and a bucket for your gear. Everything else like a spotting scope, range cart, etc. is just gravy.
If you get bitten by the bug, then I'd pickup in order:
rifle or upper for the division you choose to shoot (match or service) WOA as mentioned are great rifles/uppers
shooting jacket (as mentioned check EBay, I got a full leather coat for $60)
spotting scope - if you're not shooting full length matches a sporting goods birding scope will work fine. If you are going out to 600 yds, get a Konus or the like. (Konus is way cheaper then the other companies and just as good)
If you reload, it's easy to get started reloading as well. A 69gr over a sane charge of Varget, loaded to magazine length. That'll take you to 300 with little problems.
-Jenrick