Gravel is a multi-purpose block. If you hit it, there's a small chance (maybe 3%) that it will turn into flint, which you can use along with sticks and feathers to make arrows on a crafting table. You can also use flint with steel to make flint and steel, a useful firestarter. Netherrack, the main block in the Nether, burns unlimitedly, making it a useful torch (Just don't put any wood near it!) You can light fire near a passive mob, like a pig, or a cow, it will kill it (If it runs into the flame) and make it drop cooked meat, as opposed to raw meat. Gravel can also be used in a lava cave, if you want to cross but don't have a pickaxe to cut around the stone, because you can place the block up high, and due to the gravity, it will fall down into the lava. If you repeat this, the gravel will breach the lava and you will be able to walk across.
