Some big tips here - some may seem elementary, others not so much.
1) If you have FRS radios (the type that bill themselves as having a 2-mile radius, often Motorola), bring 'em. VERY useful, 'specially for workers.
2) Bring about 3x more radio batteries than you think you'll need. Mardens has been my go-to place for cheap brand-name batteries (Energizer E2 4-packs for $5, for example).
3) Ben's 100. Not the hippie Skin-So-Soft stuff, but the angry 100% DEET stuff. If you can't find any, Geoff's TruValue in Yarmouth will sell you the hard stuff; just ask the old guy at the counter.
4) Camp chairs.
5) LOTS of water. There's a good chance that whether you're spectating or working, you'll be in a spot that you can't get out of for a couple hours. If it's sunny, water will make you a popular person real fast.
6) EZ-UP or similar. Portable shelter from rain and/or sun is great, and you may be able to parlay your EZ-UP into sweet assignments at the start or finish line
7) Sunblock. Don't be a hero.
8) Layers. Ticks are nuts this year, and Lyme disease is no joke. Long pants and sleeves are good to start and end the day with, at the very least.
9) GPS. You're more valuable if you a) know where you are, and
know how to get somewhere else fast.
10) Cell charger. You'll be in "analog land", where your phone needs to maintain a constant connection with whatever towers it can find. Translation: batteries drain fast up there.
11) Fill your tank just before you get there. In case you have to make a "spirited" drive to the other stages, it's good to have a full tank of go-juice on tap. See Kathy's earlier post about 93-octane available just before the lodge at Sunday River.
For people on my "team", my cell number is 207.233.2370. Take a sec and add it to your phone before the event, and if you want to be REALLY proactive, text me with your name and phone number so I can add you ahead of time. There's gonna be a bunch of activity while we're up there, and it's smart to take care of our communications network beforehand.
Anyone else with experience, please feel free to add to this list. By no means is it comprehensive; just the stuff I've managed to forget in rallies past.