I'm going to start a series of posts on this topic--"essential tools" to showcase a batch of tools, components, and other products and items I use to make this whole astrophotography journey easier. The first three are must-haves in my book--links below.
1. Slip joint pliers with plastic inserts, designed for jewelry making I think. These come in handy when you need to tighten down the knurled metal screws for guide camera rings, or holding the guide cam shoe, or for tightening the tensioner on a rotator. These might work in cases where you want to tighten something just a bit more than you can with your fingers. But you also don't want to scratch the metal, paint, or plastic of whatever you're tightening. Just be careful because these are still regular pliers and you don't want to break anything.
2. I use nitrile gloves every time I'm changing filters, adjusting spacers or the OAG, and doing just about anything with my cameras. That's an obvious use, but I use these instead of the ring clamp tools I usually see as "must haves". I use these when I need to remove filters and spacers that are stuck, and the gloves allow you to unstick these without applying a lot of pressure, without squeezing one side of a spacer so much that the adjacent sides bow out and make it worse. They're even grippy enough to unstick those pesky super-slim M42 to M48 spacers.
3. Real gaffer tape, the expensive cloth stuff that will hold things down but won't leave any residue. Get the real thing, not the cheap stuff. I use this to hold cables together, to tape cables to the mount or the side of a camera. It's as permanent as you want it to be, holding whatever you need to hold until it's time to tear down your gear. Then it just peels away, and you can reuse it.
Non-marring Plastic Jaw Soft Touch Pliers