Minecraft wiki entry for Defeating_a_Nether_fortress, associated text: At least an iron sword, or an axe (or both) if you play Java Edition
A bow
At least a stack of arrows (or one if your bow has Infinity)
At least a full set of iron armor with one piece of gold armor (optional)
A pickaxe, stone or better, preferably iron or better
At least 1 golden apple (optional but recommended)
Highly nutritious food, such as cooked porkchops or steak, at least half a stack.
At least 2 stacks of cobblestone (or blackstone)
At least 2 stacks of torches, or bring coal so you can craft more
A crafting table, a chest and a furnace to set up a temporary base (optional)
At least 16 logs for crafting
Potions of fire resistance, or totems of undying (optional, but useful)
A shield
2-4 buckets (if using cauldron, have a few filled with water)
A cauldron (optional, does not work on Bedrock Edition)
Flint and steel to light your portal if it's destroyed
10 obsidian (optional, to make a new portal)
A respawn anchor (optional, to reset your spawn point)
12 glowstone blocks (enough for 3 charges of the respawn anchor). Can take more (optional)