Ask exploding heads

Really depends who you're fighting.

Realistically, as romantic as swords are, a battle would probably include military weapon. That could be a longbow or a polearm. If you were fighting a plate armored opponent, you'd probably want a warhammer or something similar that could be effective against plate.

As for armor, depends on your weapon and who you're fighting. If you're fighting a bunch of peasants armed with sticks and you've got a longbow, then you probably want to stay light. Chain mail would probably be overkill. If you're going up against someone who is armored, you kinda want to fight fire with fire and be sure to have the best protection you can get too.

Another question is about whether you're mounted or not. Being on a horse changes battle dynamics a lot. In antiquity, horses weren't bred that could carry an armored rider. That came a lot later.

If I could have practically infinite ammo? Of course I’d bring a modern rifle and handgun. If I had a limited supply, I’d probably bring a crossbow. I figure it would be easier to resupply with the materials available at the time

A crossbow. I have exactly zero practical experience with any melee weapons, especially polearms, and I don't have any skill on a longbow, leaving the crossbow as not only the simplest weapon available, but also one I would be somewhat familiar with using due to experience on modern firearms. I would also stay away from the early firearms appearing at the time since a crossbow is more accurate and reliable, as well as more foolproof.

Regarding armor, I'd likely go with heavy cloth armor and chain mail since plate armor would be more restrictive than helpful considering I would stay away from the front.

This and then spin it like fidget spinner