Barrel

Barrels are a key starting block to expand your island. Fill a barrel with 8 saplings to compost dirt. Fill a barrel with water (when it rains) and put dust in the barrel to make clay. Water buckets can also be taken out from a full barrel.

Barrel recipes
Combining fluids in the Barrel with items can create blocks and items.

Be beware that lava can burn wooden barrels!

Table copied from http://ex-nihilo-minecraft.wikia.com/wiki/Barrels