Ken,
Look in the FAQ for a thread about what must work on your 80 for it to start. The thread includes a list of some basic electrical parts that are inexpensive (e.g. fuses, fusible links, and relays) to carry as spares. That's certainly a good place to begin.
For me, one of the most important considerations is being able to diagnose a problem when it occurs, especially when it's on the trail. I've read many threads here on Mud about guys who have run into a problem and then aren't sure what the root cause is. They don't know what part they even need, let alone if they or their buddies have one along on the trip. So the real question is, what do you need to isolate a problem when it happens. I say at a minimum you need:
1) FSM mechanical manual
2) FSM Electrical Wiring Diagrams
3) A multimeter, a few feet of insulated wire, and electrical tape
4) Five wrenches: 10mm, 12mm, 14mm, 17mm, 19mm (combo open-end + gear-wrench preferred)
5) A ratchet, a couple of extensions, and sockets in same sizes as above
5) Four screwdrivers, including small and large versions of a "+" and a "-"
6) Needle nose pliers, regular pliers, and wire cutters
7) A hammer and a pry bar
Obviously this list can be vastly expanded, but these are the basics. To this I'd add one more key ingredient: knowledge of your vehicle. (This one costs only your preparation time; no money or weight.) If you know how your vehicle works when it's running well, it's a whole lot easier to figure out what's wrong when it's running poorly or not at all.
