Bone

Bones are items primarily obtained as drops from skeletons and fish mobs.

Mobs
Skeletons, wither skeletons, skeleton horses, and strays may drop 0–2 bones upon death.

All types of fish mobs will drop 0-1 bone upon death, except salmon, which will drop 0-3 bones upon death, depending on the size of it.

Fishing
Bones can also be obtained by fishing as part of the junk category. The best chance of catching a bone is achieved without the Luck of the Sea enchantment, yielding a 1.1% chance.

Wolves
Using a bone on a wild wolf has a $1/3$ chance of taming it. Bones cannot tame a hostile wolf or a wolf that has already been tamed though can be used to attract the attention of the tamed ones.

Trivia

 * As with sticks and blaze rods, bones are wielded as a tool instead of an item.