Weather is going to be up to 60 degrees on Sunday. Start getting that gear together. Maybe clean your rifle? (It's a thought...)
Any old pistol, rifle, and shotgun will do, if this is your first time. (Well, you'll REALLY want your rifle to be semi-auto, but other than that, you can make everything else work.)
I started shooting Multigun with a Bushmaster AR-15 (Shorty-AK version), a Glock 34 with standard mags, and a Remington 870 pumpgun. Did just fine in Limited division...
...just bring ammo, and very importantly, a way to carry it. Being able to carry an extra rifle magazine, enough mags for 40 rounds of pistol ammo, and ~24 shotgun shells (not necessarily all at the same time) is important.
If you can move left, right, forward, and backward safely while holding a firearm pointed downrange, if you can reload safely while holding a firearm pointed downrange, and if you know how to keep your finger out of the trigger guard unless you are actively engaging targets---then you know how to be safe in Multigun competitions.
So c'mon out and give it a try.
(On an uplifting note for the rest of us: Betsworth won't be there this Sunday, so someone ELSE has a chance to win for once!
)