Utilities
Respirator: Yes, you need one. Laugh all you want about how nice spray paint smells, and about getting high on the fumes. But in the long term, spray paint fumes are quite toxic. Wear a respirator. It’s a critical investment in your future health. And besides, it conceals your facial features should you have a fugitive situation. If nothing else, at least wear those cheap dust masks like the dentist wears.
Gloves: Often overlooked! But wizened old graff writers insist, they got health problems on their hands from not wearing gloves. It’s also been said to cause kidney failure. Paint is toxic. Wear gloves! Fingerprints are also a major risk: wear gloves!
Clothes: Don’t wear distinctive clothes when painting, and don’t wear paint-stained clothes when not painting.
Vehicle: Bicycle
Magnets: The amazing can silencer! Major hardware stores sell these circular magnets than can fit right on the bottom of the can and keep the ball-bearings (“peas”) from rolling around and making noise. Good for avoiding dirty looks.
Most hardware stores carry circular magnets like those pictured at left. Most also state the force of attraction, typically between 20 and 40 pounds–more than adequate.

BONUS TIP: Get a bunch of these magnets,and some heavy cord, and fashion a sort of “cat o’ nine cans” with magnets on the end of the cords, so you can hold one handle and tow 9+ silent cans. Plus it turns your palette into a weapon of self-defense.
Intercom: Helpful!
Climbing Gear: Needed to access high locations. Besides the usual, look for the “home emergency ladder” which has hooks for tossing up and latching to fire escapes, and also works well for getting down from high places.