The easiest way is to use a cartridge ROM dumper such as: Retrode, Flash Boy, GBxCart RW, RetroBlaster 2.0, etc. There are also a lot of DYI devices using Ardu

The easiest way is to use a cartridge ROM dumper such as: Retrode, Flash Boy, GBxCart RW, RetroBlaster 2.0, etc. There are also a lot of DYI devices using Arduino and other popular boards.