I am looking for specific aid, clothes, junk items, or special "costumes" with which companions can interact when you're in build mode or when waiting.
- Codsworth can wear a bowler hat.
- Dogmeat can wear wraparound goggles.
Dogmeat, when waiting, will play with a teddy bear if he has one in his inventory, and if the dog house is presented, he will rest there.
Cait, while waiting, can be seen taking chems if she has them in inventory (same with Nuka-Cola, but I haven't tested it yet).
There must be much more stuff like this, and I didn't spend the time needed with every companion to dig deep enough and uncover these details. So what else do you encounter in the game?