Hey, new poster here, but I figured I'd throw my 2 cents in...
As far as supplements go, I'm always very skeptical, but also very curious. I've tried a lot of stuff after it has gone on the discount table due to an upcoming expiration date or sale or something. I always use the basics like multi-vitamin, fish oil, digestive enzymes, and probiotics. In the evening I like my ZMA and Glutamine (They both just seem to help me wake up feeling less sore).
Recently, I just started CrossFit and I also run a good amount to prepare for Navy OCS. Therefore, I began playing around with some "endurance" supplements. I started with a product called Xtend, and felt it helped. I would say that I can run about 10-15% harder/longer when I'm using this. It is basically just BCAA's, glutamine, and citrulline malate. I don't know which of those 3 is actually working, but have since bulk ordered all 3 ingredients, and now concoct my own mixture with no flavor or filler. I suspect the BCAA's are the most helpful.
Another new one I've tried is beta-Alanine. This feels like it's doing something (my body tingles) and I've noticed some endurance benefits when I take 2-3 g preworkout.
Seeing as I won't have access to these at OCS though, I'll probably ween myself off.
You should probably start with BCAA's, as they are the most proven.
Most preworkout drinks contain caffeine and other mental focusers, which I enjoy, but probably aren't the healthiest.
Hopefully you don't waste as much money as I have through the years