If you really plan to be gone in the parks open to close, then a big breakfast is worth cooking, get you ready for the day. Plus you have a fridge to freeze water for bringing into the parks; can prepare snacks to bring too (individually wrapped cheese, kept in a cooler with the frozen/cold waters works well) or brown bags as someone else posted, which saves $.
The trick is to not overbuy: if you are only doing breakfast, plus a late-night snack (i.e. save the ice cream bars for home rather than the park) then buy just that. If you know you will have at least one day that is just pool/shopping and not in a park, then buy food just for that day. Or order out as others have suggested. You can always buy more if needed, that way you will not be dumping a full fridge. FWIW.
The trick is to not overbuy: if you are only doing breakfast, plus a late-night snack (i.e. save the ice cream bars for home rather than the park) then buy just that. If you know you will have at least one day that is just pool/shopping and not in a park, then buy food just for that day. Or order out as others have suggested. You can always buy more if needed, that way you will not be dumping a full fridge. FWIW.