One supplement you absolutely cannot go without?

I’ve tried lots of supplements over the years and none have had a lasting impact. Those include:
- Creatine
- Magnesium Glycinate
- L-Theanine
- Ashwaganda
- Lions Mane

I must admit, I do travel a lot for work so the routine of taking said supplements can be affected.

I’d like to ask the question… what supplement has had the biggest noticeable impact on your life and you now cannot go without having it?