The only time when it's acceptable to give a nerd a flower.
Altoid tin alterations are pretty popular among the hacking community, but this one takes it down in size. Using the Altoids Slim tins, Instructables user Joshua Zimmerman put together these bite-sized LED flashlights for under $5. With just a tiny bit of drilling and soldering, you could easily assemble a handful of these in an hour or two.
The Hungarian Forint is used in very large quantities ($1 USD = 218 Ft) so the government recycles a few tons of it every year. After shredding it and bundling it into bricks, the currency is shipped to charitable organizations to help with their heating cost.
UK not-for-profit Eggs for Soldiers built a life-size tank out of 5,000 cartons to help raise awareness for its upcoming March Fourth Help for Heroes Campaign.