This article is from the Car Audio FAQ, by Ian D. Bjorhovde (ianbjor@mobileaudio.com) with numerous contributions by others.
*Electrical tape*
Make sure you get some that can withstand extreme temperature
ranges.
*Wire cutters/strippers and crimpers*
Get a big pair with stripper holes precut for individual wire
sizes.
*Angled screwdrivers*
Makes taking dash and rear deck speakers out a lot easier.
*Multiple size screwdrivers, both flathead and Phillips.*
Magnetic screwdrivers can be a big help when trying to get screws
into (or out of) tight spaces.
*Various wrenches, pliers, and socket sets*
The specific sizes you need will depend on your vehicle.
*Metal drill and saw*
You'll need these if you need to modify your vehicle for new
speaker cutouts or to accommodate a new head unit.
*Hot glue gun*
Good for putting carpeting or door panel trim back in place after
modifications.
*Razor knife*
Helps for detailed modifications of door panels or carpeting,
especially when installing new speakers.
*Wire*
(see Section 2.3).
*Soldering Iron*
Makes excellent connections, but can be messy if not careful.
*Shrink wrap or flex tubing*
Good for protecting wire, especially in the engine compartment.
*Multimeter*
Helps to diagnose installations.
*Extra hardware*
Screws, nuts, bolts, connectors, etc.
*Fuse puller and extra fuses.*
In addition to the fuses for your stereo system, check your car's
fusebox to find the various sizes you'll need. Also, you can use
needle-nosed pliers to pull fuses.
*Wire ties*
Helps to tuck wire away in otherwise exposed areas.
*Small light source*
A flashlight will do - you just want something that you can poke
around the innards of your car with.
*Tape measure*
 
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