Crimping tools. Don’t cheap out on them. They really cheap ones will pinch you. The medium cost ones will leave you with wires pulling out when you least expect, usually during a match. Get good ratcheting crimpers that fit the lugs you use. Incidentally, the lugs we sometimes get in the KOP have been horrible for fitting in our crimpers. I haven’t checked this year, though.
Buy spade lugs in a variety of sizes in boxes of 100. They’re cheaper that way and you’ll go through a lot. Remember to consider not just the size of the lug where it goes under a screw, but the size of the wire that goes into it.
Get a good set of wire strippers. The ones with a notch for each size of wire work well, but be sure you get ones with all the sizes you need. Some of them don’t have the smaller sizes that we run into on our robots. Even then, you will occasionally run into small wires that can’t be stripped with those. For that I suggest Ripley Miller strippers. They are like a scissor mechanism with a notch in each side. A screw acts as a stop to set the size, but with a little practice, you can do it by feel and strip even the smallest wire without nicking the wire. Ripley Miller is the name of one company that makes them, but other people make them as well. Not expensive, but handy to have. Don’t bother with “automatic” wire strippers](http://www.parts-express.com/automatic-wire-stripper-with-cutter--360-627). They are for people who are stripping one size of wire all day. I’ve found them to be of little advantage in the field.
Links are examples to give you a picture of what I mean. Not an endorsement of where to buy them. You can get them anywhere you want.
You’ll want the basic hand tools, a good set of screwdrivers. Socket set, or nutdrivers. (Metric too, for those studs on the PDB) Small screwdrivers come in handy. Find one that works well with the Wago connectors and don’t loose it. It’ll make life a lot easier.
You’ll want a good VOM to measure voltage and resistance.
Large and small wire cutters - diagonal style.
If you use heat-shrink tubing (there is some in the KOP this year) you’ll want a heat gun. Matches, lighters and soldering irons just don’t do as nice a job as the heat gun.
Speaking of soldering, if you know how to solder, a pencil style soldering iron and some rosin-core solder will be handy for making reliable connections. Sometimes you just need to extend a wire and soldering can do the trick.
As for learning, any basic electricity textbook will give you the basics. Then study the Robot Rules for this year, as well as the diagram that FIRST usually puts out each year for the control system.