Hi folks!,
I just added a new page to the Lakka Wiki https://github.com/libretro/Lakka/wiki/Emulation-Tips-&-Tricks
On the new page you will find two tables, the first one is about the bios files needed by the Lakka emulators. The second table is about the rom filename extension used by the emulators. Both tables are order by SYSTEM so you can easily find the bios of the system that you want to emulate and the rom filename extension used.
Remember, you have to find and search each ROM and BIOS on internet. Lakka does not include any BIOS or Commercial ROMs.
Enjoy