I am going to explain to you why the Spirit Level is the best tool that you can have in your belt. First and foremost, it is a double threat, and two tools in one always belong on the belt.
The Spirit Level is a bottle of perfume that also acts as a level. Levels are the most under-appreciated tool in any handyman's arsenal. They help to insure that things are, well, on the level. Art Lebedev has combined the usefulness of a level with the good smell that only perfume could bring.
The resulting Spirit Level is the best invention since the clawed hammer. I know one belt that's getting a new addition soon.