B12 is the most important one. I've started getting some strange "tingling" in my arms a while ago, went to the neurologist, got a prescription for a higher dosage B12 and it went away. I was supplementing B12 already, but it wasn't regular.

Some other supplements:

- D3 (complemented with a "SAD Lamp" [0] in winter, can recommend)

- Omega 3-6-9

- Magnesium + B6 (helps reduce cramps during/after heavy training sessions)

- Vitamin C + Zinc when feeling that my immune system needs a boost (after traveling/flights)

https://examine.com/ is useful to get a quick look at the aggregated/summarized research for supplements.

[0] Random link with some explanation: https://psychcentral.com/reviews/sad-lamp