My very favorite!
a soldering iron (regulated) with a customized tooltip. Created from a piece of thick copper electrical wire with a flattened tip, like a mini spatula.
Great for finishing prints, finishing retraction leftovers, correcting little irregularities, welding pieces together, filling gaps (not pretty, but useful sometimes) and...
best part for me: first layer big print with lots of support lines; the start or end of the line can be melted to the tape (cold bed) when they tend to curl up.
I print a lot with a 0.8 nozzle and stuff like XT or Woodfill and there the first layer is trickier to put down.