bread and butter vs room and board

bread and butter

noun
  • That which is central or fundamental, as to one's business, survival, or income; a staple or cornerstone. 

  • Used other than figuratively or idiomatically: see bread, butter. 

intj
  • Said when two people walking together are temporarily separated by an obstacle in order to indicate that they belong together. 

room and board

noun
  • A place of lodging with daily meals, usually provided in return for rent or other considerations. 

How often have the words bread and butter and room and board occurred in a corpus of books? (source: Google Ngram Viewer )