To mangle a saying, "Too many tools are never enough." I'm always buying more clecos and having at least three cleco pliers is a good idea. Otherwise, they are always on the other side of the longest piece between you. Get a half-dozen or so aluminum yardsticks. I've used them, along with cleco sidegrips, to space bulkheads accurately and so forth. Rules, squares, calipers - none of the kits have them but they are the thing that will be in your hands the most.
Also, start stocking up on electrical tools. Invest in a good soldering station and crimpers, a pro-type wire stripper, crimpers, and flush-cut pliers. Don't use the latter for anything but wire, ever! And get some training; soldering correctly is just as easy as doing it wrong but you need to be sure you know the difference.
The last thing is a good fastener tool set. You want both metric and english, combination wrenches (I like the ratcheting ones but they won't work in tight spaces so get the standard kind, too), sockets in at least three drive types with every kind of extension you can afford (but no magnetic tools), and allen drivers, both hand and socket. You'll find discussions in the forums about good torque wrenches. I'd start with an inch-pound click type and later, for the engine, get a foot-pound version and also a beam type.
Every time you turn around you'll find something in a difficult to reach place and find yourself buying a specialty tool. Crows feet, close quarter ratcheting screwdrivers, 90-degree drills, and so on. Don't worry about not having every possible tool before you need it, ingenuity can get you by some needs and it usually doesn't take long to get the tool you need from our excellent vendors. Also, recognize that some 'needs' are for convenience; I tapered the spar reinforcements in the tail of my -6A using a hacksaw and bringing it down to final with a vixen file ... but it was much easier doing the same for the wing spar using a bandsaw and belt sander (somehow not as satisfying, though). Anyway, the process is fun, so relax and don't worry too much about your tool set at the beginning.