This is a small, cheap easy to build LED flashlight. Most simple one on instructables. Cost is about a dollar.
Step 1: Materials
Step 2: Construction
First, take the sandpaper and scratch the negative side of the batery until it is very rough. The solder will stick better like that. Then warm up your soldering iron and solder the negative LED lead to the negative side of the coin cell. The negative lead is the short one. Then, bend the positive lead up 45 degrees so when you press it, it turns on.
Step 3: Use It
These are good for well about everything. Put them in glove boxes, first aid kits, camping or whatever.