As others have told you, dining plan is not available offsite, but for the most part, you will pay less for your food if you buy it out of pocket anyway. There is a calculator
https://www.distripplanner.com/ that can help you to figure out your cost for dining out of pocket, compared to what it would cost for the dining plan. Additionally, we buy gift cards through Sam's Club where we get a $500 gift card for $480, so we save a bit more money this way.
We've done the dining plan, both as Free Dining, and as paid for. It costs us less to eat this way, and as a result, we are able to enjoy more sit down meals during our trip for the same money we would have spent on the dining plan.