First, I'm so sorry to hear about your aunt. {{{hugs}}} to you and your family at this difficult time.
I haven't taken a vacation yet and had to incorporate my South Beach eating lifestyle. I'll be at Disney in just over 2 months and I already have most of my ps's in place and plan to eat according to my program the entire time. I'm definitely bringing snacks from home (nuts, a few lc candy bars if I need them, etc.) We have buffet breakfasts scheduled most mornings so I can have a verity to pick from and see the characters too.
We'll do counter service for most lunches and dinners and I don't think I'll have a problem taking the bun off a hot dog or burger and I've got a listing of several places at MK and Epcot that have sugar free desserts if I feel so inclined.
All in all, I'm pretty upbeat about being able to stay on program and hope I am successful. I'm not sure which program you are following but if you have your mind made up, it shouldn't be too difficult to stay on plan.
I hope you are able to have a good trip.