Okay, I guess we're officially 'old hat' at this now, so here's a few tips for next years intrepid souls:
Pimping your Tuk Tuk: Definitely get the Roof Rack, and paint job provided by the Adventurists. We welded and painted our own and it basically burned a day to save very little money. The paint jobs that other folks had done for them looked great, and had a lot of detail, so just go nuts on your design and let them do it for you.
If you want to make some mods yourself, I absolutely recommend EXTRA LIGHTS. Mount a couple up on your roof-rack and one on the front. You WILL end up driving at night despite your best intentions, and extra lights can mean all the difference when that darkened whatever jumps out of the road at you.
Extra Horn - Our friends hooked up an extra horn and put the button for it in the back seat so the passengers could express themselves - great idea!
Honkies - Our friends also scored a smashing hit with their array of 10 honkey horns taped to the running bars. Kids loved them, adults loved them. Everyone came up for a honk. Great way to make friends!
Gas Can - don't be a cheap ass, just get the extra can. Preferably one that holds at least 7 liters. You really will run out of gas - trust me.
Funnel - that gas tank is at a funny angle so a curved funnel will really come in handy. We ho-jived one out of a soda bottle and ended up with petrol stinking digits for most the race.
Bungy cords or straps - really useful for tying crap on. You can get them in India too, so don't feel like you have to bring them - it'll just save you time the first day.
Happy Colors - We had an absolutely amazing reception almost everywhere we went, and in part because our TukTuk was bright Pink! People loved the festive easter-egg feeling and kids just went nuts. For our future travels we're definitely painting in bright happy colors. Never once were we asked for bribes or harassed - on the contrary, everyone just laughed and came by to find out who these crazy people were. So, I'd really recommend happy colors for a happy time.
Tarp - we bought a big yellow tarp the day it poured like hell in Pondicherry. It was great for keeping our stuff dry, and good for keeping the rain out of the back of the Tuk. It also came in handy keeping the freezing wind off us in Darjeeling and over the pass into Kathmandu. You can quite easily buy one in India, and undoubtedly cheaper than at home.
Things we didn't need:
A lock for the TukTuk - nobody stole it. Just our sandals and our gas can when we forgot it in the Tuk overnight. The steering column in the Tuk didn't really work, but what the hell, it came out fine. One night we got really paranoid and disconnected the sparkplug wire so it wouldn't start, but I think that was just paranoia. I mean, who's gonna get away in a bright pink TukTuk without getting spotted?
An extra vehicle - we'd talked about having a 'chase van' but in the end we were all happier off just blazing along in our TukTuks. It was helpful, especially in the beginning to have Don on the motorcycle zooming ahead, but we separated about half way up and had no real problems without our scout. The Tuks fit 3 people just fine, and we all felt like a team of 3 was better than a team of 2 for changing off driving and having fun in the backseat.
A stereo - there were just a couple times when I wish we'd had tunes, but most the time it's so damn loud with all the honking and the two-stroke engine chugging away that more noise would have been unwelcome. Still, on a couple rough patches it might have been nice to have my favorite song from the Muppet Movie to lift our spirits. So, I'd say if you get it, it might be nice, but you won't miss it if you go without.
But most of all, just wing it. It'll be fine, you'll have a blast, and whatever you forgot will make a good story when you get soaked/lost/break down/robbed/whatever. Just go for it!