K.C.
I haven't been to DisneyLand, but we frequent Disney World. :)
Bring your own stroller and load it up with all your stuff that you will need. You can bring food and drinks into the parks, you are not supposed to bring a hard cooler in. We usually bring a soft cooler or just food in the backpack (sandwiches, leftover pizza, snacks, etc) I will also usually freeze one juice box and then pack others so the frozen one will keep the others cool and then my daughter has a little slushie treat for the afternoon. We go a lot so it would cost a fortune to buy food each time, if this is your one big vacation many of the walk up food places are not that expensive. It is usually about $8 for a cheeseburger and fries. Depending on how much your 4 year old eats the kiddos will most likely be able to split a kids meal (the mac and cheese is so yummy!) the kids meals come with the main meal, grapes, carrots, and a drink. So it's quite a bit of food. My almost 3 year old can't even come close to finishing it at her hungriest.
We also bring in water bottles, there are water fountians everywhere and they are easy to refill throughout the day. We just bring our Minnie Mouse or Princess one so DD still feels like it's disney water.
Some people will suggest leaving for a little while, we never do. Even when staying the whole day. Our little one loves it so much she will either nap in the stroller or just skip nap for the day. You spend so much money to be there, I suggest staying every second. :) My 2 1/2 year old still naps about 3 hours every day, but on Disney days she just powers through. She will usually rest (not sleep) in the stroller for a bit in the afternoon, but by the time the parade is over she is ready for more rides! You know your kids better than anyone else, but I don't think leaving is necessary. :)
It will be busy, you will have a blast!!
HAVE FUN!