Add memory to your Arduino projects by connecting an external flash memory IC via SPI. I found this useful for playing back sound and buffering larger amounts of data before sending them to a host computer.
Note that this is code from 2015 and the M25P by Micron has reached end of life. However, I suspect that pin-compatible SST25VF family by Microchip might be a drop-in replacement. If you enjoy comparing datasheets or have a SST25VF chip to test, let me know. ;)