Here is my list of essential tools.
1. A good pair of snips and or pliers. You are going to have to cut a lot of filament.
2. Scotch brite heavy duty sponge the one with the rough green side. I use this when filament sticks to the extruder heads go in with the rough side while it's hot and keep those things nice and clean
3. Canola oil. I was getting lots of filament jams now ever 3rd or so time I change the filament I dip the end in the oil and haven't had a jam since.
4. Rubbing alcohol. Good for cleaning up hairspray or whatever you use to keep your prints on the bed or just cleaning the bed
5. Plastic putty knife scraper. For getting under stuck on prints or cleaning gunk off the bed or for getting a smooth kapton tape to lay down. I use mine constatly
6. Xacto knives these are mostly for after the printing is done but they come in handy for cutting kapton tape and other things.
7. Lube for your machine. I use super lube synthetic grease to keep things moving smoothly
8. Nitrile gloves. They are disposable and you will be using chemicals like acetone that you don't want to make a habit of getting on your skin.
9. Digital caliper. Lots of settings and prints need exact measurements.
10. Binder clips. If you need to hold down some wayward tape or keep a new glass bed from moving around binder clips are great for easy adjustment and being cheap.
11. Flashlight. you need to see what the hell your printer is doing and the lighting inside is much to be desired get a good flashlight you are going to drop a black screw in a black background eventually and a flashlight will save your sanity