Fun hack: "Joule Thief"
I am not sure who coined the term Joule Thief, but I like it. It is used to describe a simple voltage boost circuit that "squeezes" otherwise wasted stored power (W) in a primary (non-rechargeable) battery, in the last lag of the battery's life where it suffer from voltage drop off.
As far as I know the majority of battery powered devices do not use a similar circuit to help extend the useful life of non-rechargeable batteries even in the excessively common low current demanding mass market device like TV remotes and such.
So here is one how to make a joule thief page by Alex Smith. Another make a Joule Thief from Big Clive, and you can watch a video podcast with Evil Mad Scientist Laboratories and Bre Pettis (if you don't just become obsessed with Bre's hair, it just creeps me out for some reason). Finally, there is another Joule Thief booster circuit that is available in kit form and uses two transistors, out of a total of 7 parts for ~70% efficiency. That could be almost invisible with SMT parts. Here is some more information from White LED Drive Circuit by Dick Cappels and Joule Thief wiki page from David Wagner.