I've been playing with SD cards recently, reading up on how SPI works, the SD cards' command protocol, and the structure of the exfat filesystem, and I've now got it all hooked up so that I can browse the filesystem, load files, and run code from SD cards. Awesome! No more messing about with EEPROMS! As always please do comment if you're interested in more details, instructions, or code, or if you've done this as well, it's always good to exchange experiences! Since making the video, I published the code in a kind of walkthrough tutorial format here on GitHub -