DD16 and I went to WDW in August 2010 (wish we were going this year, too), stayed at POP with upgrade to regular DDP (1cs, 1ts, 1 snack per day). We found we could easily share a breakfast at POP's food court, then share a lunch later in the day. The food court has a platter with eggs, meat, hash browns, beverage that was more than enough. We had refillable mugs, so used the "free" beverages with breakfast (coffee, iced tea) and took the meal beverage (bottle of water) to the parks with us. Most cs places in the parks have huge combo meals, too... double burgers with enough fries to feed a horse. We are big eaters in my family, but sharing our cs credits saved us money. We aren't big snackers, and had 4 snack credits left at the end of our trip.
ALSO: We brought some cheap plastic storage containers to carry in the backpack. We are always too full to enjoy dessert after a ts meal, so we took the desserts to go in our own containers (which seal tightly) and enjoyed them while watching the fireworks or back at the hotel. Saves on snack credits, too!
Get glowsticks at the dollar store before leaving home. I usually buy the round tube that has 10 or 12 sticks and connectors, and I buy a couple of them. CHECK THESE IN A SUITCASE... different TSA agents feel differently about passing these through security; I've had them passed through, and I've had them confiscated

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If your kids are young, steer them away from trinkets and souvies. Pressed pennies are a good idea, and it gets to be a treasure hunt to find the machines. Souvies are never a problem with us... just say no. I don't have any good suggestions if your kids can't handle that. I guess try to avoid shops as much as possible, or bring stuff from the dollar store at home. I read about a family that successfully negotiated out of the souvineer situation by bringing stuff from home and setting up a "morning surprise" each day. Tinkerbelle brought such wonderful toys each morning, straight from the dollar store! For older kids, who won't buy junk and blow their money right away, give them a set amount and tell them that whatever they don't spend, they can keep. Works wonders with older kids, especially if they have a "vanilla" visa or master card. It can be used anywhere at home, too!
Water... yes, iced water is available at any food court or cs, but it's time consuming to stand in line, and I had a couple of places insist that they can only give out one cup per person, so everyone had to wait. We bought Bobbles before going on our trip, and they worked well with tap water. Also, the hole in the top is big enough to slip ice cubes through, so we'd fill the bottles with ice before leaving in the morning. I got two bobbles with filters, shipped from JCPenney, for about $15 (but I know I had a coupon or free shipping or some special deal, can't remember what.) I guess Britta is now doing an individual, filterable bottle, too.
I have a friend who gets free gift cards through her credit card points program. She gets them in $5 denominations (for places like Kroger, Dunkin Donuts, whatever is local in Orlando) and leaves them for mousekeeping instead of a cash tip. Yes, they are free for her, provided she doesn't need the points somewhere else, and I think any mousekeeper would rather have $5 in cash, but this works for them.