I think first place would go to my hand chisel. I used that thing for everything, from prying tile, wood, and carving. Of course, my measuring tape, hammer, screw drivers, and electric drills were invaluable in completing the project.
After reaching the end of the most laborious construction project of my life (which took nine months), I returned home to my place in Austin in my pickup truck loaded with tools. There was no room to park my vehicle in the garage with all of the construction paraphernalia that I had acquired throughout the project. My garage floor was a mess and I needed to come up with a solution.
I decided to construct some shelves with some leftover pieces of wood. I found it funny that in order to store my tools, that I would need to use them to build once again. I couldn't seem to escape construction!
I bought some heavy duty mounting brackets. I designed the layout, found the studs behind the wall, and drew the mounting points using a level. Then once the mounting brackets were installed, I simply placed the 2x12 planks of wood on top and secured them in place.
The project took a Saturday afternoon, but I was thrilled with the results! Finally I could easily store my tools securely in an organized garage (& park my truck!).