consider the Sole Survivor: 

• incessantly making pre-war pop culture references that no one understands 
  
• telling their companion(s) stories and they think they’re just a really creative person who’s making them up but really they’re just retelling the plot to one of their favourite tv/radio shows
• getting cravings for food that doesn’t exist anymore and complaining about it for days or trying to make dishes by substituting in stuff from the wasteland and it coming out absolutely horrible but eating it anyway because in some small way it reminds them of their mother/father and/or spouse’s cooking
• teaching their companion(s) card games they played pre-war that were otherwise lost in time
• just trying to balance who they were before and who they are now by not living in the past but bringing little pieces of it to the present so they don’t completely lose themselves to life in the Commonwealth