Hi Michele,
Thank you so much for visiting the Disney Parks Moms Panel with your question. We on the panel love helping guests to plan magical vacations!
I have good news for you. You can bring food and drinks in a backpack or small cooler into the Walt Disney World theme parks. My family and I do this every time we head into a theme park. We always take bottled water in with us. My favorite tip with this is to freeze one of the bottles of water. It will keep the other bottles cooler, and be deliciously icy to drink! I also like to carry in snacks that I know my family will like. When we are waiting in a queue, or simply when we have been walking a lot, having a snack at hand is wonderful.
Please do note that there are some
restrictions on personal items that can be brought into Walt Disney World theme parks. The most salient of these for your question is that you cannot bring in glass containers (although glass containers of baby food are permitted) or alcoholic beverages. There is also a size limit on coolers and backpacks. You can click on the link that I provided for specifics information on size limitation and other restrictions.
I hope that this information is helpful for you, Michele! Please do let us know if you have any further questions.