Breed two cows with wheat.

Catch and cook a fish!

Use a saddle to ride a pig, then have the pig get hurt from fall damage while riding it.

Use a Grindstone to get experience from an enchanted item.

Eat nothing but Kelp for 3 days.

Smelt an iron ingot.

Stay underwater for 2 minutes.

Bake a cake using wheat, sugar, milk and eggs!

Gather all 16 colours of wool.

Attack and destroy a monster.

Smelt wood trunks using charcoal to make more charcoal.

Dry a Sponge in a Furnace.