A mace, good food, and most importantly patience. The Swamp is very hostile and dangerous. It rains almost all the time which will mess with your stamina, there are several mobs in there that have a very dangerous poison that could potentially one shot you if you're hurt.

Take it slow, pick your fights, and work your way to your objective. The enemies aren't like greydwarves where you can just pace yourself mid fight, they will just rush at you and attack.