The sulfur block should be used to create gunpowder.

In real life, sulfur combined with charcoal and potassium nitrate is used to create gunpowder. Potassium nitrate could be replaced with bone meal in Minecraft, and combining it with sulfur and charcoal blocks should result in the creation of gunpowder. This would allow even Peaceful players to obtain gunpowder without relying on hunting creepers.