To the experienced builders. What are the absolutely neccessary tools to build a reliable trued wheel? The wheel will be a 700c wheel for a standard road bike.
To properly true and tension a wheel:
You can, of course, jury rig a Truing stand as others have mentioned, and you can build without a way to measure the tension on the spokes. Without a lot of practice and skill, though, your wheels will be less than perfectly strong and straight.
You should use a thread locker on the spoke nipples. Ideally, Spoke Prep from DT Swiss, or Linseed Oil, which acts as a lubricant until it dries, but acts as a thread lock once it's dry.
The book at the end of the list will teach you the theory behind how a wheel is built and why, and the lacing patterns, and what works best, and why.
There are definitely more sophisticated tools for this but in my mind the essential kit includes (1) the right-sized spoke wrench, (2) a flathead screwdriver, (3) grease for spoke threads, (4) the front dropouts on an upside-down bicycle with brake pads for truing, and (5) lots of patience if you haven't done it before.
All of this assumes you have a rim and hub with the same hole count, along with correctly-sized spokes and enough spoke nipples.