Minecraft wiki entry for Complete_main_adventure, associated text: 2 stacks with cobblestone or other block with blast resistance over 4
A full set of diamond armor, with at least Fire Protection IV.
A piece of golden armor (boots or helmet are recommended) to defend yourself against piglins
An iron or diamond sword
A bow and a stack of 64 or more arrows (if your bow is enchanted by Infinity, bring only one arrow)
Two pickaxes: a stone pickaxe for mining netherrack and a iron/diamond pickaxe for mining harder materials.
A stack of steak or cooked porkchop, or another good food.
Golden apples (optional) for emergency healing
Shields are recommended to deflect damage.
Potions of Fire Resistance to defend fire damage