Back in the earlier years of computers, prior to standardization, manufacturers of expansion cards put the BIOS commands for the device directly on it, stored in ROM.
Mr. Williams: Duh, there isn't one! It's BYOB, the bios is ON it!
Common expansions of the acronym include:
Bring Your Own Bottle
Bring Your Own Booze
Bring Your Own Beer
Bring Your Own Beverage