String

String is an item used to craft various items or blocks.

Mob drop
A spider will drop 0 - 2 string upon death.

Block drop
Cobwebs will drop 1 string when broken with any sword besides golden swords.

Fuel
String can be used to smelt 0.5 items in a furnace or 1 item in a forge.

Brewing
String can be placed into a cauldron.