My favorite tool by far is my Milwaukee screw diver. Traxxas techs use the Milwaukee 2401-22 screwdriver. It allows you to set the clutch very low so you won't strip your plastic threads. The trigger / variable speed control is really good too, so you won't melt the plastic threads. Plus it has plenty of torque when you need it. The screwdriver is not the cheapest, but it is elegant and a perfect fit for people doing repairs and upgrades on RC vehicles. My Home Depot has this drill and others on demo at times. You may want to take a look. I even bought some small sockets and adapters for removing the big wheel nuts.

LED flash lights.
Magnetic dishes for holding loose screws.
I am far sighted, so I use an OptiVISOR for close up work.

Plano parts containers - typically found in the fishing section at WalMart.

Body work: Xacto knife, reamer tool, body scissor, Shoe Goo and Duratrax DTXR1210 repair tape are a must. Get extra and use it early.

It doesn't hurt to have a couple small tweakers - small flat head and phillips head screwdrivers. You will run into a non hex screw from time to time.

volt meter, IR temp sensor from Duratrax. Lipo balancer, Team Integy makes a Lipo Voltage Checker / Alarm.

A couple different needle nose pliers, Xuron Nippers

Soldering iron, flux, solder >50watt if you plan to work with motors and battery connectors

Here are a few little thing that often get overlooked. Get some good Velcro. I use Velcor brand Magnum Force 2 RC car contact cleaner, Epic blue oil for bearings, Lithium grease for rebuilding servos, Black grease for metal gears, Dynamite DYN5405 tire glue, Losi shock O-ring grease. Blue Loc-Tite - liquid and stick.

We have used Loctite two part epoxy a couple times.

I have used the RPM bearing blaster a few times with the contact cleaner. Seems to work ok. The jury is still out on this vs. replacing bearings. There is a good YouTube video showing this tool.

My disclaimer - I have only been at the RC thing for a year now, so I am sure there are better ideas out there. I would like to see some feedback on this as well.