I can't find the thread or the post, but I once came across a post on Touring about the neat stuff you can find in a discount or dollar store to use ion a bike tour. The list included lights. While I wasn't able to find dollar store bicycle lights, I did find some items I can use:

Insulated lunch bag
packets of instant oatmeal
zip ties and bungee cords
bicycle cable lock

Any other goodies to look for?