The joystick in the back there looks a heck of a lot like an Atari 2600 joystick. Maybe there was some way to connect the 2600 joystick to a Commodore 64.

kagis

Ah. Apparently the Atari 2600 and the Commodore 64 used the same joystick interface.

https://www.facebook.com/groups/atariage/posts/10161218803290255/

Does C64 joysticks work on the Atari 2600+ unit? I have a couple laying around. Thought they might work with 7800 games?

The original Commodore 64 used “Atari” joysticks.

kagis

Sounds like the Amiga also had the same interface, given that these joysticks are frequently being advertised as being for the Amiga and Commodore 64:

https://www.ami64.com/c64-joysticks?page=3