Aside from all the "regular" things you'd use a flashlight for when ashore, on a boat you'll also want to have one handy so that:
- You can inspect the bilge
- You can inspect your shaft log packing
- You can inspect your thruhulls... all your thruhulls, especially if item #1 has suddenly become important...
- You can signal other boats
- You can bungee it to something astern to serve as an emergency stern lite (don't ask)