Colecaciferol (vitamin D) supplements as my levels drop otherwise.
I'm taking a general vitamin supplement while recovering from recent surgery as well as trying to eat as well as I can when someone else has to do ALL the food prep.
I think I tried glucosamine and chondroitin with no apparent improvement in my joint issues in the 2000s when my mum got into it, she had arthritic issues related to cancer and post-cancer treatment. I don't think she bothers now, but they switched her off the horrid post-cancer drug (which gave her horrid joint issues) back to tamoxifen cos she got on with it OK.
My joint issues are joint dysplasia from my syndrome so my wrists, elbows, shoulders and hips aren't quite formed correctly which results in undue wear and tear + other issues.