Protein is the biggest thing, that and knowing what your doing in the gym. I’m not big in to a ton of supplements I drink whey shakes, use a multivitamin and fish oil and that’s about it.
A lot of my workouts revolve around functional fitness, running, rucking, lifting, and working out in armor. Right now I’m on a cut cycle (trying to loose fat after a bulking cycle) so my workouts revolve around a lot of cardio right now. When I bulk I tend to eat more carbs and protein along with a more lifting based work out program. It’s the fastest way to gain mass but you also gain fat so you need to mix in cut cycles to keep yourself trim and functional.