I have still never used a tension meter. I built many wheels before tension meters were invented, so I haven't felt the need.

I do like having a dishing tool, but I don't consider it essential. I've occasionally used two stacks of books or whatever what was on hand.

The most essential tool is a set of excellent spoke wrenches.

If lacing wheels, it's nice to have a modified screwdriver for driving nipples in. I just file the sides of the blade so the middle sticks out. I did this with a super-cheapo screwdriver. Works well.