Hi, Linda! Welcome to the Disney Parks Moms Panel! I'm so excited to hear you have started planning your vacation, woo-hoo!
Guests have plenty of freedom on how they choose to use their
dining plan entitlements. It is not possible, though, to trade two quick-service credits for one at a table-service location.
On the bright side, if you have an extra quick-service credit at the end of your trip that you will not be using and would like to receive some packaged candy to take home as gifts or to be eaten later, you can do that. My family and I brought home very cute Disney-themed PEZ dispensers that we gave away to nephews and nieces; they travel extremely well and everyone liked them. They can be found at resort gift shops and some food courts; they all make fantastic souvenirs for kids.
Linda, I hope you find this answer useful. Please come back with more questions; we are eager to help!
~Desiree