I did an Appleseed in November. I learned a lot about shooting, as well as learned that I really stink as a rifleman.
Don't bring a Mosin-Nagant unless you are a glutton for punishment. You will turn your shoulder into meat quickly. An Appleseed shoot is ~200 rounds per day, and if you are not familiar with the Mosin-Nagant and 7.62x54R cartridge, let me just tell you that you don't want to do that to yourself. The recoil (especially from the M44) is very...shall we say...signifigant... Additionally, you really need a semi-auto with a 10-round magazine capacity for most courses of fire. You won't finish most courses of fire (time limit) unless you hold the Guinness record for cycling/reloading a Mosin-Nagant.
I used a Yugo SKS (M59/66). That was a mistake. It didn't fit me well, is rather heavy, and had poor sights and a poor trigger--I didn't realize really how bad until I was trying to shoot well with it. That said, it would be a better choice than a Mosin-Nagant. Also, it may work better for you than for me, and it definitely isn't a wasted purchase.
If you shoot your AK well, bring it. You probably won't do the best with it, but it will be OK (this is a learning exercise now, not a competition). One of the kids in my group (15-year-oldish) shot rifleman qualification with an AK. The instructors were very surprised, but this illustrates that it is possible.
I agree with the 10/22 recommendation. I have not used Tech sights, but they come highly recommended by all I have heard from. This will be the most cost-effective platform you can bring. They're accurate and no more than $40 (for the "good match-grade stuff") .22 ammo will do you for the weekend. Compare to $120 of cheap ammo for a .30 cal. Remember, you will go through about 400 rounds in the weekend. You could put the saved $80 (or more) toward the 10/22.
I plan on going again in 2008. However, this time I'm bringing an AR15 with a peep sight. I just want the "realism" of a larger cartridge and am willing to pay the extra expense for ammo.
Tips:
You need a semi-auto with at least 10-round magazine capacity. This is what the courses of fire are designed for. Many are 10-round strings or fire 2 rounds/magazine swap/fire 8 rounds, and are timed (actually time-limited). This really stinks with stripper clips or 8-round en-blocs (M1 Garand). I frequently didn't finish courses of fire trying to load the SKS from stripper clips. Actually, a Garand is a good choice (good sights, good trigger) IF you can reload it like a madman. As I said before, unless you are the speed demon of bolt-action, you will not finish most courses of fire with a bolt gun, as well as have to regain your firing position after cycling the bolt.
Bring good ground cover, like a carpet remnant about 2x your width.
Bring a military-style sling. This is a MUST. You can get a surplus Garand/M14 sling from a gun show for $10 or less that will fit most rifles. You can probably order them cheaply on the Internet as well. "Hunting" style slings are no good for this.
Bring at least 4 (empty) magazines, the more the merrier. You want to spend your designated prep time getting into position and dry-firing on target, not loading your magazine.
Bring some bottled water and food/snacks.
Bring sunglasses (prescription if you need them). It was BRIGHT in the morning/early afternoon. Also a hat, or you will get sunburn.
Bring your own staple gun and staples. Light duty is fine.
Unless you are used to shooting 200 rounds from the prone position daily, BRING ELBOW PADS--the non-slip baseball type without the plastic cap. If you don't your elbows will be bloody on the first day and intolerable by the second.
Practice prone position, and take a few dry-fire shots from it daily for about a month before the shoot. This will REALLY help you out.
