Here are my current tools that I prefer to use with my 3D printing. You might have some other ideas, but I recommend building a kit containing these items and whatever else you find works.
Any cutting board should do. This is a self-healing cutting board I’ve found while at a hobby store, and the measurement markings are convenient for checking sizes of prints. Keeps you from destroying the table you are finishing, painting, and sealing the prints on.
3D Printer Spatula:
Used for removing prints from the print bed. I saw this particular one on a recommendations list for tools, and it has made a huge difference, compared to the painter’s scraper that I was trying to use before. With the scraper, I had to constantly replace the tape on the board (about every other print). With this spatula (and good tape), I can go for a dozen or more prints without having to replace the tape. The spatula flexes and gets under the edge without digging into the tape with the corners.
Painter’s tape is essential to printing with PLA if you don’t have a BuildTak plate or similar on the print bed (most do not). You use it to cover the print bed to provide a good surface to adhere to the print bed, and in the case of a print-bed attached with screws (like my Colido DIY), it covers the holes for a print. When the tape gets damaged, you need to replace it.
I recommend going with the actual 3M brand tape, it works much better than whatever off-brand tape I used before. The other tape required replacing much more frequently. Maybe some other tapes work as well, but so far 3M works for me.
This tool makes removing excess material easier, while being able to follow the edge of the part. The deburring end rotates freely as you drag it along the part edge.
Used for precisely cutting off some material. I don’t use this tool nearly as often anymore, as the deburring tool is better for what I had been using it for. Also, the next set of tools are easier and safer to use for this purpose, but aren’t as widely available.
Cutting Tools (Chisels):
I was introduced to these when touring someone else’s 3D printing lab, and knew that these were the tools I had been looking for. Various shapes for cutting different parts, and the harder metal and thicker geometry makes the much better than an exacto blade for cutting/prying support material off of a print. Since I’ve gotten these, I’ve rarely used the exacto knife. Also, it’s probably not supposed to be use this way, but I’ve found that the flat back end can be tapped with a mallet for some situations where it would be unsafe to simply keep applying more pressure.
For cleaning up parts in some other ways.
Hobbyist’s (dental) pick. Good for cleaning up some items, particularly in small spots. Nowadays I mostly use it to help remove support material. The fine tips get damaged with use, so you will need to replace this one periodically.
I mostly use these to pulling hot filament off the extruder end when changing filament on the printer, and for holding parts while coloring or sealing them.
The cutting pliers (left) I use for cutting filament to change filament. The needle nose pliers (middle) I often use for cleaning filament off the print head, or removing support material by crushing through it and pulling it off. The last pliers are better for large pieces of support material (I don’t use it as often).
The level is good for leveling the table the printer is on, and then for making sure the platform is also level. If your table isn’t level, trying to calibrate your printer will be more challenging. Eventually I may want to upgrade to a multi-axis level that i can place on the print bed for easier leveling.
These fall more in the category of something used for calibration and 3D modelling aids. If you are designing something to interact with something else physical, you likely need good measurements to inform your model. Starting out you’ll probably use a ruler, protractor, and measuring tape. Eventually, though, as you try to deal with interfacing parts, you are gonna need a digital caliper. Mine switches between mm, decimal inches, and fractional inches, though I mostly use it in millimeter mode. It takes a slight bit more knowledge to use, but I recommend taking the time to learn how to use one properly.