Minecraft wiki entry for Thunderstorm_survival, associated text: Sword or axe (preferably iron, diamond, or netherite).
Trident, Channeling enchantment can be used for thunder mob farming, while Riptide enchantment can be used as fast transportation or go to higher place easily.
Shovel
Pickaxe
Bow or Crossbow
Arrows, carry 1.5 times as many as you think you will need. Even if you have a bow with Infinity (Optional but recommended) or Crossbow with Piercing III or better, bring at least 10 arrows.
Shield (in your offhand slot)
Iron, diamond, or netherite armor.
At least a half stack of a cheap block, such as Dirt, to build pillars or blockades to escape mobs.
Plenty of food, 2 types is best: one that has a high saturation value, and another that has a high hunger value.
A bucket of water, to put out the larger fires from lightning.
A few things such as a Lantern or a Torch so that you can light up anywhere that you need to prevent mobs spawning.