I'll add a few..

When you get a new body, keep all the extra lexan you trim off. Lots of uses for it and you can heat it and mold into almost any shape. I usually ream a post hole in a flat section and then cut a diamond shape or even some flames around the hole and ca glue it on top of the new body to reinforce the post holes. It stays clear and looks cool. You can also take an old tired body and cut any piece you need and shoe goo it on the inside of your new body to reinforce any section you wish.

You can also use an old body as a template for your new body when cutting post holes, engine and fuel cutouts (assuming body styles are the same or fairly similar). I never trust those pre-marked guides. Put the old body inside the new body before painting and trace your outlines with a sharpie.

If you've got crud around your plug, a quick pit fix is to turn it upside down and squirt fuel up in there to flush it out.

Get some velcro tape and put about a 3" strip up front between the body and chassis on both sides. This keeps a lot of dirt from kicking up inside your ride, and most times you won't even need a front body clip to hold the body on.

Fuel line on a zip tie makes a great cap puller for your fuel tank.

Get a small leather hole punch and make 2 or 3 evenly spaced holes in in the center line of your tires to let dirt escape.

In a pinch, you can wash your air filters with mild/diluted dish soap and then oil them (lightly) with vegetable oil.

When replacing broken parts, go ahead and buy two so you have an extra on hand for next time. Stock up on "perishable" items when your budget permits.

Never use threadlock on plastic.

If you strip a screw, you can file or dremel a notch in the head for a flathead screwdriver.

You can bring brake discs back to life by rubbing them on sandpaper. Lay the paper on a flat surface and run the disc over it a few times.

Never wash your wheels/tires under running water. Water + tire foam is bad.

Make sure all your nuts/bolts/screws are tight before you run.

Never wear a cape. You ever seen the Incredibles?