Flights, room, tickets and food are the biggies. Check rates and discount codes on Orbitz. I have booked twice with them and it ended up being cheaper than booking directly through WDW. You can add the reservation to your Disney account and get all the benefits as if you booked directly through Disney.
Orbitz offers the same special discount rates Disney releases but every time I check they have a code for extra off (usually 15%) and most Disney resorts are included. So if Disney has 15% off values Orbitz offers that discount and you can stack their code on top of that.
If you want to save a few dollars more go to Ebates and use their Orbitz link. That will get you some money back.
Orbitz also sometimes has discounts on tickets. Right now they have buy 3 days get 2 free. I go through Ebates and get a little $ back on these as well - and Ebates sometimes has 20% cash back on tickets through Orbitz!
Where are you guys coming from? Check airlines that do not charge for luggage or make sure you know the charges - a great fare might not be so great when adding luggage and sometimes even carry-ons

I love Southwest - 2 free bags, snacks, Disney automatically check you in your return flight. JetBlue is another good one depending on where you fly from.
For food I usually pack some Pop Tarts, breakfast bars, cookies, popcorn and a few other snacks (this is when those free bags come in very handy

). One year I even brought bagels! Some counter service places have huge portions so that could save you some $$. I do not cook while on vacation so we never book a place with a kitchen but if that is something you guys want you can make some super cheap meals - but that involves a trip to Publix or
Walmart.