Some good ideas here. Since we have AP we go alot here are some things we do are (some already mentioned):
1. Bring in our own snacks and beverages. I usually carry in my own soda cup (styrofoam works best) and a few cans of Diet Coke in a my bag. When we eat at counter service I just get a cup of ice and use that for my soda. My DD10 doesn't get a beverage with her meal unless she gets a kid's meal. Otherwise she gets water and I carry Crystal Light flavor tubes. She loves those. She also carries her own water bottle, on a strap, and puts flavor in that as well.
2. Another thing we did recently in the summer was when we got cups of ice at Schmoozies in DCA we noticed the ice was pretty ground up. DD10 added a lemonade tube and a little water and it was like having a sour lemon slushie. She loves it.
3. Besides getting free water and ice at counter service locations you can also get free hot water at those equipped. On cooler days and evenings I bring our own tea bags and make hot tea. Saves $2.79. I read you can also get coffee refills by showing your receipt from the same day. Hot chocolate work too. I suppose you could even add instant soup (I think they still make it don't they?)
4. Share-we frequently share meals. Just like at WDW some of the meals at DLR CS are quite large. Some of our favorite shares are: Pasta at Pizza Port or Plaza Inn; Fried Chicken at Plaza Inn; Pizzetta Salad at WTC; and Asian Chicken Salad at Pizza Port. One of our favorite CS locations is Water Water Snacks in the GC. A nice break from the day and just a little bit better food. The nachos there are totally shareable. I don't like cheese sauce so I order mine without. Only shredded cheese. Sour Cream and Guacamole on the side. Then when it's delivered (yes the bring to your table) I pop it in the microwave and melt the cheese. I've also seen parents use the microwave for warming up their own items as well.
5. Go off property to eat. Many times we stop on our way to, or from, DLR to eat. Del Taco is one of our favorite choices. Saves tons of money and better food than some of the CS choices.
6. Souvenirs-we don't buy many at DLR but sometimes do at WDW. Give each child a certain amount of money they can spend on their own souvenirs. It's amazing when they ask for something and you say "you can use your own money" how quickly they change their minds.
7. If you plan on riding Grizzle Rapids and don't want to get soaked bring your own ponchos. Much cheaper than buying them in the park and after using them you can just through them away. You can usually get them for about $1 all over. When we go to WDW I have a Ziploc that I carry our ponchos in. Keeps my bag insides dry and then I can reuse them.
8. Speaking of GGR, they have free lockers (1st 2 hours) located just to the left of the ride entrance. Keeps all your stuff nice and dry.
9. When we stay at WDW (on property) we have our breakfast in the room everyday. We buy a cheap toaster and use it for toast, bagels, poptarts, etc. We also have cereal, PB& J, fruit, etc. Saves alot of money by not having to eat breakfast out and really saves on time as well. Since you are driving bring along an ice chest as well. If you'll be parking at DLR it's nice to come back to the car after along day and have some ice cold drinks waiting.
That's it for now, if i think of more ideas I'll post them. Have fun!