The phrase "staple side" refers to a specific end or edge of something, such as a document or a booklet, where staples are used to hold it together. Full definition
The cuisine always seemed mysterious and intimidating to me until I was intrigued enough to try one of Korea's staple side dishes — kimchi. (fromachefskitchen.com)
Looking for a few staple side salads to serve at a gathering or bring to a potluck? (cabotcheese.coop)
He snips through the stomach, which has the consistency of a banana peel, dividing the organ in two, and staples each side shut. (discovermagazine.com)