There's going to be a lot of people there this year, looks like, so a camp chair wouldn't hurt - unless you want to sit on the ground. Though people often bring extras.
While there's always stoves and such around at the kitchen/fire area that can be used, if you bring an extra it won't go to waste. With 40-50 people looking to heat up water in the morning for coffee, extra stoves are always useful.
The great thing about this is that it's technically car camping. So throw whatever floats your boat into the car - it's not like you have to carry it in and out. Extra blankets, bags or quilts, extra food, that larger pot that holds more water but is too heavy for backpacking, the woodstove you bought but haven't actually used yet but want to play around with ... if you think you might use it, there's no downside to putting it in the backseat.
Heck, the first year I was there, Syb brought along a spool of Zing-It and some tools since he was just learning to splice, and Saturday afternoon some people helped him learn how to do fixed eye splices. There's lots of folks around of varying levels of experience and knowledge - so it's a great time to learn, check out new gear, try out stuff, get help and feedback ... sky's the limit!