We generally drive to our destinations, so we always pack 'snack packs' for the car. Generally we have pre-made sandwiches, chips, snack crackers, goldfish, twizzlers, granola bars, nutrigrain bars and cookies. I pre-pack everything in bowls in a small tote so they are ready to grab quickly when needed. We keep a cooler with water, milk, juice and sometimes soda. We also keep deli meat, and pre-made meals in there. I often make meals in the week before a trip, and then freeze it in single-size servings. Things like spaghetti and chili, goulash and almost any casserole work great for this. They make a quick and easy lunch or snack, or even a late supper if we had a late lunch. We've stayed at hotels that don't have refrigerators or microwaves in the room, but they often have microwaves in the lobby for everybody to use. We've even packed a small microwave when we were gone for more than a week on one trip. We just keep a cooler of ice if there is no fridge...usually ice is free at hotels anyway. We do this for camping too.
That being said, we do usually eat out once or even twice per day while on vacation...we feel that is part of our 'get away'. I just like to be prepared when we are sitting in our room at midnight and decide we are hungry. LOL
We also use our supper leftovers for lunch the next day (or snacks at night).
We flew to Disney last year and that really threw me off. LOL. We had the 'dining plan', so most of our meals were already paid for, but I still took nutrigrain bars, granola bars and various other prepackaged items. We also carried a water thermos with us everywhere we went. We didn't spend a dime on bottled water or sodas, we just refilled our thermos and water bottles (we brought from home) at water fountains.
This is a great thread with great ideas