[Fun fact!] Jeffrey grew up a nomad and will eat basically anything.

Arthur's been a drifter for several years, so proper meals are something of a special treat saved for stopping at a proper inn or establishment. He knows how to roast something over a fire, but that's about it.

Harry, meanwhile, learned to cook while in the vault -- it wasn't a strictly necessary skill, as there was plenty of pre-packaged and preserved foodstuff, but his father's friend's grandmother took him under her wing and taught him the basics anyway, as a means of passing the time.

(When he discovers how Jeffrey and Arthur eat, he's honestly kind of horrified. Harry takes over food preparation for the party effective immediately.)

Today we learned Jeffrey is the human version of a goat

jeffrey, chowing down on a radroach leg: food is a means to an end