During the discussion about mining helmet, someone suggested a torch that you can throw.

So imagine a Flare Stick that you can throw or drop into a cave system that would burn brightly for a short period of time (even shorter than torches).

This would decrease the chance of jumping into a cave full of creepers or spending a long time trying to find where that sound comes from through triangulation. The brief burning time and the cost can be use as the limiting factors to stop it from being abused.

Another cool feature is that flare can burn underwater, which means that it can help with say patching up that hole you accidentally created in the basement while experimenting with TNT. No more blindly fumbling along the bottom of the dark seafloor trying to find items you accidentally dropped.

Lastly, for a slightly more permanent solution, or just to pimp out that lava heated pool you built. Combining a lantern with a block of glass = waterproof lantern aka Pool Light !