Spoke key is the most important tool. You must have some oil for lubing your chain, so you can just use that. And a spare spoke to act as a guide for deep-v. The other tools are to aid you in the truing and tensioning process and makes life a hell of a lot easier. I would recommend getting a truing stand though even for a single build. You'll be able to sell it again no probs. You could probably borrow one too as loads of people on here have one.
Spoke key is the most important tool. You must have some oil for lubing your chain, so you can just use that. And a spare spoke to act as a guide for deep-v. The other tools are to aid you in the truing and tensioning process and makes life a hell of a lot easier. I would recommend getting a truing stand though even for a single build. You'll be able to sell it again no probs. You could probably borrow one too as loads of people on here have one.