Perfect advice above. Gun, bullets, & tag. Everything else just makes your experience more enjoyable and tolerable. Some of the extras will provide the ability to spend more time on stand.

I suspect you are looking for more ideas than the obvious three. Here are some more;
knife, binos, drink, attractant, scent eliminator, wind indicator, tp or napkins, food, extra pair gloves, calls, hat, saw for limbs, pull up rope, marking tape for tracking, radio or cell phone, compass.

I do recommend a tree stand. I spent may years on the ground and scared more deer. Once I got elevated, my success went up dramatically. If you get into a tree use a harness and consider purchasing a hook or hooks for hanging stuff.