Just went to California and DLR three weeks ago with three teen DSs and my DD, her last trip as a "Disney child."
1) We only stayed at hotels that offered full breakfast. Convenient and the cost already baked in, everyone could get what they want, including a variety of drinks (milk, juices, tea, coffee) instead of just one drink like we'd do at a restaurant. It also got kids to eat some fruit. It would be near lunchtime before anyone wanted a snack.
2) We used our Canadian Costco card, which is good around the world BTW, at Cali Costcos and the Sam's Club card I got to save on tickets and gift cards to buy gas, bottled water, case of whichever generic Powerade/Gatorade Sam's has, generic Kind bars (high levels of nuts, thus protein and fat --> Satiety), box of individual trail mix packs, and splurged on jerky bars for our pickiest eater, to ensure he'd get protein, and our biggest teen, who just needs *calories* all the time. Having these in our packs meant smaller meals or heavier snacks were all people needed to get to dinner. Dinner was always TS and basically order whatever you want because we had saved elsewhere.
At WDW definitely get the refillable popcorn bucket, an amenity not available in Anaheim (because they can't figure out how to prevent locals "abusing" it? Idk, but it was disappointing.)