They don't normally do all 3 meals "in their room." A standard theme park day (this was Universal) for my family involves getting up, putting the coffee on while I take a shower and sunscreen, coming out and getting my coffee while slicing up some apples or strawberries, pulling out cereal, toast, butter/jelly and bacon (cooked the night before) and getting kids fed as they wake up (and then getting them dressed/sunscreened - spouse handles the sunscreening). Each kid starts the day with a "main", some fruit, and some juice/milk, so they aren't starving as we enter the park. While the kids are getting full and ready, I throw together a soft-sided cooler bag with some water, Capri Sun Roarin Waters, and a soda for me and then the day's "snacks" - rice krispie treats, homemade trail mix, and fruit squeezables are common. We then hit the parks all day from about 10am-7 or 8pm (leaving at close or for our offsite dinner plan), and we normally have a single CS meal onsite - although we have also done TS if we feel like it b/c we have done the dinner/movie/golf deals. We then head to a nice offsite place to eat or if our meal/snacking was heavier that day, we head back to our room for sandwiches/smoothies.
Now, we go in September, so Universal almost always has their CS BOGO 1/2 daily plan for AP holders...and we use that on the days I want a butterbeer or a big pink donut. On those days, I pretty much bring nothing to the parks (although we still eat breakfast and dinner offsite) b/c the plan is more than enough food and drinks to keep us going all day. Sometimes we have leftover "items" on the cards to use other days...and we do.
Sometimes, b/c we have APs, we only hit the parks in the evening after having breakfast/lunch/swimming/resort activities all day (offsite, we tend to stay 11-12 days at Bonnet Creek). So, for 4-5 hours once the heat of the day is passed, we also walk in with about nothing and can enjoy and then head home for dinner. We love doing this on days there's a huge storm around 2-3pm b/c parks clear and make riding rides really easy.
Also, Magical Dining Month is always going on in Sept, so the spouse and I wear the kids out at a theme park or other Orlando activity, take them home for sandwiches (or a frozen pizza - this is a favorite for them) and smoothies and then go out ourselves to high end restaurants for a steal! And helping a local charity to boot!
PS - This plan, starting with fruit and juice or milk (and ending with nightly fruit smoothies), also keeps the kids systems "consistent" and lets me never say "no" to "crap" in parks...if they want nuggets and fries for every park meal, that's fine b/c they are eating 2 non-crap meals a day...