I'd also get a right angle and straight die grinder (don't buy the harbor freight one...they are CRAP with a capital S).
Loose those stupid drill stops that Avery throws into the kit. Instead, invest 30 minutes with some scrap aluminum learning how to drill.
I added a #30 and #40 single flute countersink (it fits in the microstop cage). Single flute countersink leaves a MUCH nicer hole (it doesn't chatter like the 3 flute does). I also added a couple of single flute deburring bits. I just really like how single flute cuts. The 3 flute is faster, though (3 times as fast in fact
and I use that quite often too depended on what I'm doing.
You're going to need a Vixen file and a decent handle for it (you COULD use a crappey wooden handle but why would you when you can get a nice rubber handle). While you're at it, pick up a set of punches (you'll need them for drilling out rivets and stuff), a set of files in addition to the Vixen file (you'll need this for fine work and smoothing out the marks left by the Vixen file), and a set of micro files. All this stuff can be had fairly cheaply at Sears/Lowes. I don't use Harbor Freight for stuff like this because many of their tools are suspect in quality. Why buy stuff twice, right? I did buy the micro files there, though. I think some of this stuff comes in Avery's kit, but I dumped it and went to Sears instead because they were WAY cheaper on some things.
You' gonna need a bench grinder. Now that I DID buy at Harbor Freight...get the one with ball bearings...it's only a couple of bucks more. You put the scotchbrite wheel in there. In fact, I ordered the coarse wheel also and put that on the other side. If you're priming you're gonig to need some sort of paint gun. Once again, you can't go wrong with Harbor Freight here.
Think ahead and setup your compressor. I have a T in mine and two seperate outputs. First it goes to a filter/moisture trap. Then one side of the T just goes to a regulator, and that's what I use to paint. The other side goes to a regulator, then an inline oiler. I use this for everything else. The extra regulator and plumbing was only, like, $20 or something. Incidentally it's a big Kobolt (Lowe's brand) 60 gallon 220V jobby. Is that overkill? Yeah, probably. But you know what, between the compressor and the plumbing my whole air system is %100 headache free and always ready to build when I am. Hell, we're building $60,000+ aiplanes (many are more like $80,000+ these days). An extra one or two thousand spent along the way for little luxuries that make building easier (especially if you're ridiculously busy like me) are well worth it, IMHO.
This stuff isn't nescessary, but it sho' is nice to have:
1) Belt/Disc sander. I have the Ryobi. I LOVE that thing. I use it ALL the time.
2) Bandsaw. I use this occasionally. Do NOT buy the craftsman bandsaws (at least not their consumer grade ones). In general, craftsman make reasonable tools. Their band saws SUCK. I wish I'd bought a Ryobi.
3) Drill press: Used occasionally, but when you need it you need it. There's NO other way to use the fly cutter without killing yourself. Also, you're going to want it to drill through tubes, and things. Craftsman's drill presses are decent for the money.
4) I just picked up a Skill jig saw. You wouldn't believe how convenient that is. Oh, I need a small piece of 2X4 to use as a shim. BuuuuzUZUZUUuzZUZZZZZZ. 30 seconds later, DONE. I use this more than you might think.
5) Get a engraving pen for marking parts (Left, Right...etc) or stock up on BLUE sharpies. For some reason, blue sharpies seem to show through primer really well. I use the engraving pen on the few parts I actually need to mark since Metalprep takes the sharpie right off. I'm lazy and don't want to remark them after I just spent and hour cleaning them.
7) If it's not in the kit, add in a rivet removal tool. Not strictly nescessary (and often I just drill them by hand), but it is convenient, though.
8) You cannot possibly have enough clamps, and you cannot possibly have enough different sizes of clamps. Quick clamps, C-Clamps, vice grip style clamps, etc etc etc. Trust me, no matter how hany you have there will come a point when you wish you had just one more. Harbor Freight is an AWESOME sorce for C-clamps. DIRT DIRT cheap.
9) I have the Harbor Freight metal vice (quick release button, rubber jaws, etc). This works really well and can also serve as a drill press vice I believe. I bought my other vice from Lowes, though. A little bit pricier, but not much though. WAY higher quality.
10) I built a couple of the EAA workbenches. I don't like them that much. They're just too small. I do use them, though. I mounted all the bench tools (except the drill press...I like being able to move that around) to one of them, and I use the other one as a general put-crap-here table. Instead, I went Lowes and bought a fire door. They're wood (on the outside, anyhow), and typically very straight (bring a straight edge and measure or borrow one from the "tool crib"). Let the door overhang the frame about 1" or 2" all around...maybe 6" or 8" on one end. This is useful for clamping things down.
I dunno...this is what I find works for me.
-John