I just purchased a Zona razorsaw from BalsaUSA for $4.65 (including the wood handle). I like this so much I may get two more in case of loss! Definately a tool you should have - nothing better at making good butt joints. Another great but inexpensive tool is a "T" pin pusher/puller. This thing is a Godsend. I use LOTS of pins as I use Titebond II glue most often. With this I have no trouble pinning spruce to my building board. Some time back I splurged and purchased a 1" x 18" x 48" balsa block building board (like Butcher Block but in balsa. I love it. I still use ceining tiles for tail assemblies and smaller jobs.

I also went to a commercial paper suppy outlet and bought a 24" x 3,000 ft roll of waxed paper (about 20 years ago). I use it when butchering deer and in building over.

Good lighting. A spirit level to make sure your worksurface is flat and level (also good at holding open rolled plans).