You can never have enough string / rope supplies. Once the stores close down you are stuck with your supply for eternity unless you know how to make your own naturally, like people did before the modern era we currently live in today.
There luckily are a few ways to make rope / cordage using just what the natural world provides us or with scrap that will persist for decades. Below is a list of methods. Not all inclusive... at least not yet.
Short quick cordage from tree bark
Cordage from deer legs
Cordage from deer backstrap
Cordage from plastic bottles! Plastic String
Cordage from leather! Leather Rope