https://www.gamespot.com/articles/far-cry-5s-companions-hang-out-but-youre-not-invit/1100-6458131/

Far Cry 5 boasts a small army of companion characters to help you take down the doomsday cult in the fictional Hope County, Montana. But what do they do on their off-hours? An intrepid investigation has uncovered that they all go to a party without you.

PC Gamer followed companions from remote areas on the map to see if they find their way back to their homes. They don't, and the real answer is much worse. Instead they head to a pizza place and just hang out together. It's at the 8-Bit Pizza Bar in the Henbane River region. This only applies to your six human companion options, so Boomer, Peaches, and Cheeseburger aren't allowed–which only makes sense, given the possible health code violations.