Much of it depends on your budget, and what you think is worth spending money on.
We prefer to stay in a value, and we are considering off-site for our next stay.
We have also decided that we would prefer to stay for 10-14 days every four or five years than a shorter trip every two years. Once you get to 7 park days, the cost of additional days is very little. The cost to stay is essentially the hotel and food costs.
We bring our own breakfast, but eat in the parks. Breakfast consists of oranges, granola bars, yogurt cups, juice boxes, etc. while we wait on the buses in the morning. The one exception is a farewell breakfast the morning we leave to go home.
We don't get park hoppers. Not only does it cost more, but we waste time switching parks.
Edit: Like others, I've purchased things I knew the kids would want before we left home. Princess dresses for dd came from Disney outlet. Disney plush toys and other items came from either the Disney outlet or JCPenney and hidden in our bags. "Mickey Mouse" would come by when they were in the tub or while they were in the parks and leave them these things.
Glow necklaces and bracelets can be purchased at the Dollar stores or
walmart. Same with ponchos.
We also brought in our own water. We would fill up with water from QS locations when convenient.
All the things you need that can be brought in the parks can be purchased ahead before you leave: sunscreen, water, hats and visors, ponchos, hair ties, mini flashlights, etc.