Mobile power supply & breadboard
-EDIT- I reread this post, and it didn't sound at all clear... so I re-wrote it.
I put this together so that I could easily move circuits around, like testing the distance the SparkFun RF stuff would reach, or as a fridge temperature logger. It consists of a SparkFun Mini Breadboard and a 3AA holder sawed out from an old toy. I wired it so that I have access to all three AA cells, making it easier to power the circuit at different voltage levels. The header on the side of the breadboard is wired (from left to right) like this: 4.5V (or three cells), 3V (two cells), 1.5V and two 0Vs, or GNDs.
The circuit show is a simple circuit made up of a Picaxe 08M, a SparkFun RF TX, and a switch to turn it all on or off. I used a rubber-band to make sure that the batteries didn't fall out.