A little late to this party, but:

most events are structured tan camos versus green camos with each side having a list of common camos to select from. So, for example, if you want to play on the tan side, you can't go wrong owning a set of DCUs, Arid MARPAT or Multicam. Likewise, for the green side, M81 woodland, temperate MARPAT, OD, etc.

It gets more complicated once you start to talk about the bigger national events - these may have much more specific camo requirements.

I have 6 of these (http://www.evike.com/products/38167/) that I purchased with a bunch of extra caps. I can fill the shell with whatever level of ammunition I want (less ammo for more range, more ammo for greater spread, etc). The info I've seen is that having the single large hole in the shell versus many holes a-la the "shower" type grenades is beneficial for launching nerf-type projectiles. I haven't actually shot any nerf footballs or foam whatnot using these shells, so I don't have any direct experience with them. I looked into getting some CO2 shells, but the requirement to have some sort of extra device to fill CO2 into and then from that into the shells was offputting.

Probably the most important thing in attending a MILSIM event is to come prepared and ready to play. Your gear and equipment should be squared away; you shouldn't have to hunt high and low for pieces of gear. You should be ready to toss your stuff on and hit the field. As mentioned above, your rifle needs to, at the very least, be reliable.

I'd also add that there are two components that are a must for any event that has a night component: a night aiming device like a laser and a flash light. You can easily get away with not having an optic of any kind, but it's important to be able to see where your rifle is pointing at night (laser) and identify targets (light).

I personally bring 2 guns to any major event I attend; a primary and a back-up. I leave my back-up in my car. If I won't have an opportunity to go back to my car I carry a high-capacity sidearm (MK23).

My other recommendation for both guns and gear is to keep things as light and as simple as possible. MILSIM events are often high intensity with few (if any) breaks. Having a lightweight set of gear and a lightweight rifle means tiring out less quickly and being able to remain effective on the field for longer periods of time. Keeping things simple means not carrying everything and the kitchen sink onto the field with you. Bring only necessities.

Fixed.

Holy crap, dude. That was an epic trip!

Sorry to have missed meeting you. Maybe in the spring I'll head up to the UP and play with you guys.

I used to always recommend that people buy a gun for its externals and features that they like, and the internals can always be modified, tuned and improved upon.

Yeah, that's great advice. I don't know how much time and money I spent in earlier years modifying the hell out of the exterior of my AEGs.

I've got more... and not just of me...

Not ashamed, I scrolled just to see the pink shirt.