Cacti have always been farmable completely automatically. With pistons in 1.7, sugar cane can now be farmed in a fully automatic fashion as well. Mobs and animals can be farmed as well in giant mob grinders. To my knowledge these are the only items that can be farmed in a fully automatic fashion in vanilla Minecraft.
Cobblestone can be farmed fully automatically using mods, or in a semi-automatic fashion using TNT. Wheat can be farmed semi-automatically on a massive scale, but unfortunately requires replanting and tilling.
What I’d like to know is if there are any contraptions people have contrived to harvest any other item in a fully automatic way without using any mods.
Answer
Aside from the things you mentioned:
Fully Automatic (no need for player’s presence):
As long as you keep the chunk loaded, you can go on an adventure while your farm is producing
- Anything that uses a smelter (cooked food, experience generators, etc.)
- Honey Bottles, Honeycomb
Fully Automatic, as long as player is within 128 blocks of farm
- Melons & Pumpkins can be farmed using BUDs.
- Mushrooms are easily farmed, since they spread by themselves.
- Eggs can be farmed
- Wheat can be fully automatic using a farmer villager
- Bread with farmer villagers
- Cactus
- Coal
- Iron ingots
- Gold nuggets
- Steak, Raw Beef, Leather (if you are lucky enough to find a mushroom island)
- Cobblestone with Wither or Ghast
- Cooked Chicken, Raw Chicken, Feathers
- Redstone, Gunpowder, Glowstone Dust, Sugar, Wooden Sticks with a witch farm
- Slime Balls
- Sand & Gravel Duplicators and Flint (actually a bug, but still possible)
- Carrots and Raw Potatoes with farmer villagers
- String, Spider Eyes
- Bones, arrows, bows
- Rotten flesh
- Seeds and any kind of 1 block flower
- Ender pearls
- Any kind of potion
- Prismarine Shard
- Magma cream
- Ghast tears
- Kelp
- Bamboo
- Sugar Cane
- Wool (dispenser equipped with shears)
- Records
AFK farms:
You may need to jam the click button, and you wont be able to play while harvesting
- Snow (at some time pre 1.15, this was fully automatic. No longer.)
- Any experience farm
- Wooden logs (any type)
- Tree saplings (any type)
- Fish, Name tags, Nautilus shells, saddles, enchatment books
- Blaze Rods
- Any kind of 2 block tall flower
- Animal breeding farm
- Dragons Breath
- Cocoa beans
- Nether Wart
- Ice with a BUD to detect the freezing water (not sure if withers can destroy ice)
- Stone (needs silktouch pickaxe)
- Any Type of Wooden Planks just craft the output of the log farm
- Glass and Panes (smelt and craft the output of the sand duplicator)
- Flint and Steel (craft the outputs of the Iron farm and the gravel duplicator)
- Mushroom Blocks
- Grass and Mycelium (although it is not technically infinite, it is practically infinite)
- Emeralds trading the output of another farm if you get a perfect villager
- Full diamond toolkit and armor trading emeralds with a blacksmith villager
- Mob heads except wither skeleton (with a charged creeper farm)
Attribution
Source : Link , Question Author : dlras2 , Answer Author : John