Pocket digital lamp

As your PDA has probably big and bright screen (if it is at least a bit modern one), it has enough light to be used as a flash light.
Now and then you will see the programs for this, but they are more or less useless. They can only turn your screen into white to get more light. If you don't need every bit of light, just run some program that has enough white on screen (Pocket Word is strongly suggested for this), and you'll have mostly the same effect.