One of my favourite things to do when I have some down time is to grab a random devkit from my pile of random devkits, and try and write some code that will run on it. I generally try and avoid existing SDKs, or installing new tools. I just want to see how little I can write and have something run on the board and have an observable output. If that goes OK, I might go overboard and start writing some little drivers for a few peripherals here and there. If it really gets out of control I might end up having written a whole new Operating System, with VGA output and SD Card support. But usually I'm OK with Hello, World on a UART or a blinking LED.