Rc Equipment

WD-40, every RC man should have some of this in his tool box, just oiled almost every moving part in my rustler; and it's like driving a new car
A power drill that can accept sanding bits and has variable drill speeds, sped up the process of modding the chassis and unscrewing the screws to oil so much easier.
A good charger, really speeds up charging, rather than waiting overnight for a batt to charge. It takes only 45 minutes
A good Lipo battery or two, the difference between a good Lipo and a bad one is tremendous,the Gens Ace Lipos are really good value and high quality.
Solder, You never know when you might need to solder up some connectors or resolder your motor to your esc after disassembling your car.
A propane torch or a soldering iron, I personally just use a propane torch to melt the solder, but a soldering iron will be a good investment
Traxxas Connectors, these connectors seem to work well, and they haven't shorted out so far while driving through puddles and such.
Ca glue, or beadlocks, Ca glue is good for regluing a tire if it starts to come off, and beadlocks allow you to quickly switch tires.
Not a temp gun, I say that if you can hold your finger on the motor/esc for at least 3 seconds, you aren't running too hot.
Not a heat gun, you can use an old hairdryer to heat that shrink tubing, and a propane torch for anything else.
Hex Screws, if you haven't converted over to using hex screws, they are great, no more stripped screws, hexcrews offer conversion kits for most vehicles, the A.P. screws are waterproof so you don't have to worry about rust.
Not a dremel, unless you need finer control than with a drill using a sanding drum
Shock oil, for tuning your shocks so they work better
A sealed diff, this makes a huge difference if tuned with diff oil, less unloading of the diff (Wheel with less resistance spinning faster), but still allows you to have a very good turning radius.
A brushless system is one of the first upgrades you should buy, it offers higher speed, efficiency, and reliability than a comparable brushed system.
For the brushless system you should probably convert your bushings to bearings. Full Force RC sells full bearing "renewal kits" at a reasonable price.