firmware.bin or firmware.signed.bin (to update the firmware);
firmware.debug.bin or firmware.debug.signed.bin (if you want to telnet to your SmartEVSE to see debug messages);
rfid.txt (if you want to bulk upload allowed NFC tags for the RFID reader);
You should only flash files with those exact names. No need to flash spiffs.bin for versions 3.6.0-RC1 and newer! No need to rename firmware.debug.bin anymore for versions 3.6.0-RC2 and newer! Signed firmware is verified to be original and can be handled by versions 3.6.2 and newer.
NOTE: "Choose file:" uploads only work with http connections, and will fail with https connections!