It may not be the most glamorous or exciting part of an electronics project, but your device will need some sort of a power supply. In fact, there’s a good chance that you’ll either need a 3.3 or 5.5 V source of power, which is easy to obtain… Just go to your local retailer of fine electronics, and ask them for the needed 3.3 or 5V battery.
Oh, that’s right, there’s no such thing.* You could wire 2 AA batteries together in series for 3V, or 3 for a close enough 4.5V, but do you really want your project dependent on a voltage source that may or may not be adequate? One solution would be a DC-DC converter, either a boost converter if you need more voltage, or a buck converter to step it down.
Alternatively, this dual regulated power supply lets you input between 6.5 and 12V DC, and magically produces both 3.3 and 5V supplies via a pair of voltage regulators. This means that you can use a standard 9V battery with your project. The device even includes a 9V connector if that’s what you choose.
*Yes, I know, you could use a rechargeable USB power supply for 5V, though I’m not sure where you can get a portable 3.3V supply. Feel free to ping me over the head on Twitter with any obvious solutions I’m missing!