The NUX Mighty Lite BT Mini Modeling Amp is a guitar amplifier combo with 3 Watts of power. It's extremely compact, highly portable and has three channels on board (clean, overdrive and distortion) as well as digital reverb and delay effects. There's an auxiliary input too, but you can also stream music to it via Bluetooth!
 
This mini amp even has built-in drums and a metronome to help you keep time when you're playing. The tempo of the metronome and the speed of the delay can both be adjusted using the handy tap tempo function. The amp can be powered by a 9V DC adapter, but it also runs on 6 AA batteries which means you can use it almost anywhere.