I don't tend to use many purpose built 'fidget toys' but I have found that I definitely benefit from something small to fidget with in a pocket.
Currently my favorite for this is this unicorn toy (coin for scale)
It was the 'surprise toy' in a bath bomb I used and I find his squishy body to be perfect to mash between my fingers to help me concentrate. ..that's probably why all of the painted details are almost gone now. One of my favorite things about this as a fidget is that when I inevitably lose it, I'm not overly worried about it. I got what I paid for in the bath bomb in the first place, I consider the toy a bonus. And I can always go get another one! side eyes at the small herd of unicorns on his dresser