With its thickness of 1.4mm, this Faber-Castell 131432 is an extremely fine mechanical pencil for drawing on rough surfaces. Unfortunately, it is currently unavailable, but hopefully it will be back in stock

Sostrene Grene has great small but good metal rulers for less than €2. For that money, there are at least 6 of them lying around my workshop, conveniently hung on magnets everywhere.

With these angle rulers you can easily and accurately measure and mark out your work.
Every millimeter has its own line, so you can't make a mistake and you can easily pull your ruler along your work. The end piece is adjustable, so you can re-align it if it is no longer square.
You need a 0.5mm pencil for this ruler; if you order the A version you get it with it; the B versions are just the ruler. I have the 40cm B version myself.

This square is actually for machinists, but precisely because of that also very suitable for woodwork; the squareness is much more accurate in that class and therefore works easily; It is only 100x70mm, exactly the right size to set your saw blades or guide rail / fence properly square. It is made of steel, so rock solid.

As with any measuring tool, these also come in many different price ranges and qualities. This one from Parkside (Lidl) is extremely suitable, certainly as long as we are not working under laboratory conditions. There is also a more expensive version, but I only see the difference in color. The other one says that it switches off automatically, but mine does that too. I can definitely advise against the one from Action (same price)!

Regularly available on the website with a 50% discount!

Dial gauge holders are also available in various prices and qualities.
This holder is used to place the dial gauge against something to then measure. Perfect to check whether you have mounted the linear rails of your cnc correctly.
The system where everything is operated with 1 button is cheaper, but I find it inconvenient to use