Saving Money in (and out of) the Parks
Disneyland is not cheap. Kids ages 10 and up pay "full fare," and those between the ages of 3 and 9 aren't much cheaper. Our one-day tickets limiting us to the use of just one park (we chose Disneyland rather than California Adventure, which is being overrun this summer by folks wanting to experience the just-opened Cars Land) cost $249 for the 3 of us. Multi-day tickets and "park hoppers" (which permit switching between parks during the day) would obviously drive that price up considerably.
That's one reason why I recommend staying in a close hotel -- we spent probably a total of more than 11 hours in the park, and that's something we could only have done if we had stayed in a hotel that close the night before and the night after. We invested in the hotel (a bit) so as to maximize the value of those tickets.
Beyond the tickets and lodging, your other major cost component is food. Most hotels along Harbor Boulevard have refrigerators and if you're driving in, you should definitely pack breakfasts and other foods in a cooler and use the fridge. Some hotels have free continental breakfast and some don't (ours didn't), but my sense is that even those who do have a fairly minimal breakfast, low on the protein, and so it's probably worth your time bringing some. (If you're flying in, I have read that Vons offers free delivery, one-time, if you sign up with them.)
As for saving money on food in the park, good luck with that. Like I said, I didn't think the food prices were terribly outrageous, but they're not cheap. At "counter-service" restaurants, you are more likely to be able to mix and match meals and may find that a single adult meal may be sufficient to feed you and a kid.
As always, bringing waters and snacks will help reduce the mid-morning, mid-afternoon, late night munchies. Not totally eliminate them, of course, and part of the fun of an immersive environment like that of Disneyland is to try the food.
One way I tried to extend the Disneyland Resort experience without spending money on tickets was to experience more of the resort. So after we got settled into our room on Thursday afternoon, we wandered around Downtown Disney (the shopping/dining/entertainment district just west of the parks) and the Disneyland Hotel. We ate at Tangaroa Terrace (a "counter service" restaurant overlooking the Hotel's large pool area), then soaked in the atmosphere at Downtown Disney. ("Soaking in atmosphere" means enjoying the crowds, something my wife definitely would not do.) I am very much against window-shopping as entertainment, but the LEGO store has some amazing Disney-themed structures and lots of LEGOs for freeplay, and wandering through the World of Disney store is a good way to let off some of that "gimme gimme" steam your kids are likely to have. (I didn't want to spend our time in the park itself being in shops.)
On that note, I'm sure you all have your own rules for spending money our trips, but for what it's worth I let each kid spend no more than $15 of their own money, and they were perfectly happy with that. Letting them know that the trip itself was their gift drew no whining on their part.
Another way to extend the experience is through a character meal. There are character meals in the parks themselves, but you can also have character meals in which a variety of Disney characters stop by, interact, and pose for pictures. The meals are, again, on the expensive side (especially for what tends to be a buffet), but if your kids are particularly into a character, the opportunity to have a relaxed (and air-conditioned) interaction may be worth the cost compared to waiting in line 30 minutes in the park. We had a Sunday morning buffet at the Storytellers Cafe at the Grand Californian Hotel. The buffet was pretty good, Little Boy Blue (and Miss Mary Mack, a little) enjoyed the characters, and it gave us an excuse to go through the hotel, which is a themed wonder. Again, you don't need to have a meal here to wander through, but it was a nice way to extend the Disneyland experience before heading home.