Hi, Lauri! Welcome to the Disney Parks Moms Panel! I'm so excited to hear you are just a few months away from your trip!
If you have an extra quick service meal 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, for instance, you can certainly do that. If you have a table-service credit that you do not plan on using and you'd prefer to grab a quick service meal instead and carve some more time out for one last attraction before a park closes, that is absolutely possible. Let's say you can always downgrade from a higher rank type of credit to a lower one. However, it is not possible to do it the other way around, or "upgrade" by accumulating a number of snack credits to trade for a quick service one.
However, let me tell you that trading a quick service meal for three snacks at the end of our last stay worked out really great. We brought home very cute Disney-themed PEZ dispensers that we gave away to friends and family; they travel extremely well and nearly everyone likes them. They can be found at resort gift shops and some food courts. Disney Mints are also great since they come in metal containers and travel really well too. My nephews and nieces have started their little PEZ and Disney Mints collection; they make a fantastic souvenir.
If you need more detailed information about Disney Dining Plan options, you can find it
here.
Lauri, I hope you find this answer helpful. If you have any more questions regarding your trip, please visit us again. We love to help!
See you real soon!
~Desiree