We have amplifiers that will drive that speaker, and this tutorial shows how to set up a mobile sound system for a bike:
https://learn.adafruit.com/ride-rock-di ... r/overview
The only FM receiver we have is part of the FONA embedded cell phone though (
https://www.adafruit.com/product/1963), and we don't have any Bluetooth devices that transmit data fast enough to work for music.
To run a 6-ohm 5W speaker at capacity, you'd need about 5-1/2v across it, and the class-D amplifiers we carry need about 2v of headroom beyond what reaches the speaker. That means you'd need about a 7.5v supply to get everything the speaker can put out. Running it at a lower voltage and power level won't hurt anything, but you won't be able to blast it as hard as the speaker will stand.
We have LiPo cells and chargers for them, but only the 3.7v kind. For a battery with higher voltage you'd need to check somewhere like Pololu.com (they do robots:
http://www.pololu.com/category/54/batteries) or diydrones.com (airframes:
http://store.3drobotics.com/t/parts/rc- ... /batteries).
Choose a battery, then find the right charger for it. Different battery chemistries need to be charged in different ways, and using the wrong charger is dangerous.