I don’t even really know if you can count this as a mixer since all it can do is control the volume of 2 sources and then output the audio from both sources to one output. But hey, if you’ve got a pair of devices with 3.5mm audio jacks and you want to give it a try, nothing is stopping you.
Two iPods is the most obvious solution, but I think there are others. I mean, when I was in high school, there were a few kids who had found a way to remove the lid from their CD player and still make it play and they’d “scratch” them like a record and it would make similar noises, so a pair of those might make for a decent set for a DJ on the go.
I have no idea if the Micro Mixer DJ-4 comes with the audio cables or not, but all it does is connect two devices via headphone jack and provide a couple audio knobs and a single output to connect to a stereo or speakers. You can get one for about $135.