1) A tool box. If you didn't already make a tool box in month 1, start now! I recommend a Japanese style toolbox. There's a good video showing how they work here:
Why? Because they're relatively simple, they can be made out of commonly available materials (1x10 and 1x2, for instance), and they don't have many difficult cuts. If you're careful making your cuts, you shouldn't need anything but wood, nails, a saw, and a hammer to put one together.
You could also build a Dutch-style chest, which is my personal preference, but that involves some angled cuts, dealing with hinges, and things like that. It's still doable with these tools, but it's not easy.
2) A bookshelf. If you follow this link, you'll find some photos of a book case from the book "The Anarchist's Design Book". While it would be a lot easier with a couple of extra tools, you could build something quite like it with the tools you have now. Cutting dados with a ryoba is a pain (I've done it), and you won't be able to do tongue-and-groove joints for the back, but you can make something quite similar with a saw, a chisel, and a hammer.