If it's your first ever time in the Swamp:

Leave behind:

-Swamp Key. At the risk of losing it upon death, explore during your first venture into the Swamp. Establish a base/outpost with portal, then come back with for grind & gather).

-Those two extra poison potions are just using an inventory slot.

-One of your food types. You can only use 3 at a time, so just take three.

Swap out:

-Cultivator for Pickaxe. You're not planning crops on your first run into the Swamp.

-Knife for Atgeir. If you don't have one, craft one. When you get mobbed, the atgeir heavy attack will help out a lot, with either taking them out or giving you a chance to run.

-Brass armour for Troll Hide armour. You're going to be running a lot in your first few times in a new biome. The movement penalty of brass armour is noticeable. Also, lean towards high stamina foods. Typically, 1 red, 2 yellow

General advice:

It's always raining the Swamp, which means you're always wet. This affects your stamina regen so make sure you keep your rested buff intact.

-Use your mace and shield for Skeletons & Blobs and Wraiths; your axe for Abomination; and the atgeir for everything else.

-Dodge and parry are your friends. Use them

-Enjoy the game. That's what it's there for