Hi Rachel,
You could upgrade your basic dining plan to the
deluxe dining plan, but there is no way to just add a few table service meals to the basic plan. But no worries, on any version of the dining plan you're welcome to pay for food out of pocket. For example, even if you're on the dining plan, you can certainly go to a table service restaurant and pay for your meal with cash, credit card, etc.
Also, if you're on the dining plan, you can supplement a meal that you're paying for with credits. For example, you could get a meal with a dining plan credit, but add an appetizer and pay cash for that. You have a lot of flexibility this way.
Good luck with your planning. Please let us know if you have additional questions.