Assume that you need to log some of your readings from the input pins of your Arduino Uno (or MEGA, etc.) dev board which needs to work standalone. The proper way is to store the log in an SD card ...

Arduino UNO Micro SD Data Logger A serial communication channel was set as UART and the data received from this channel was written to the SD card as a text file with Arduino UNO and Micro SD card ...

Setting it up is really easy.