Please correct me if I am wrong everyone, but the
DDP was not meant to be used to share a single meal. That being said, I know that the castmembers will work with you all whenever possible. Firstly, do not book reservations for buffet places. It will be a waste of a dining credit for you both. (Unless you REALLY want to see Winnie the Pooh at Crystal Palace or Playhouse Disney at Hollwood and Vine).
Next, I suggest to have only one person order and to ask for a second plate (as is usually done, but not to directly ask for the option to split the meal in the kitchen before serving). When the check comes, you will only have to charge a drink as a snack or just to the room and 1 TS credit.
If they won't accommodate that, I would suggest bringing a small soft-side cooler for your backpack to place your doggy bags in.
I have had to be on some pretty peculiar diets (medical reasons), where I needed to eat around 5 times per day. I carried around my tupperware in my backpack and ate when I felt like it. The chefs were so understanding that the ones at my resort even sourced out special foods that I could eat (iodine-restricted diets are awful, and I needed hard-boiled eggs to survive).
My other recommendation is that you all eat the morning meal before you leave the room (they have places to buy quick breakfast fare at the deluxe resorts, but there is also a Publix grocery store less than 5 miles away). This will help your DDP credit last you longer.
Good luck!!! (and remember, it is a magical place where the castmembers do try to make your every wish come true).