I know there is debate over whether the dining plan is “worth it” or not. I personally think that depends on the season, # of character meals, deals, etc. (see if it’s right for you here). If you do decide to go for it here’s a few hints that aren’t advertised to help you get your money’s worth. Always check with a Castmember to be sure of what’s available before ordering.
1. For Quick Service they don’t differentiate between kids and adult meals. So if you are grabbing breakfast 2-3 kids can share 1 adult QS meal. Since most plans have 2 meals per night stay it can be helpful to share often. We usually got 3 meals for 5 of us (DH ate his own, me and the 3 kids shared 2).

The meal the kids got their own were the kid’s power pack. A meal of yogurt, goldfish, apple bar, juice, etc. They loved those more then anything (those are in the cooler hidden by beer at Art of Animation, also available at Sunshine Seasons in The Land). The make your own pasta at places is huge and can feed two adults with a salad.
2. An entree generally comes with 1 or 2 sides and a dessert. Instead of dessert you can often get another side (although some places like China in the World Showcase at Epcot give you an extra bottle of water instead of a side/dessert). This is also helpful if you are sharing meals.
3. At some QS you that are more cafeteria style (resorts) they offer you 2 sides at the station, like chips and coleslaw with a sandwich. They don’t tell you that you can grab snack item from the coolers instead, but you often can. Check with a cast member to verify. With my giant sandwich I would get a large cup of strawberries and hummus and veggies, we would end up using them as snacks later. Fruit is also a dessert, you can get something like 1 banana or a huge container of pineapple.

4. You can exchange QS or TS meals for 3 snacks at places that serve food.

In other words, you can get 3 snacks at any restaurant, but that’s a pain (3 orders of fries?) or at Starbucks, the Confectionary at MK (all the fudge you could eat!) , the Land store at Epcot, etc. We had someone tell us to go to a QS restaurant and exchange our meals for snacks then go back to a store to use them on candy, that’s not true and I wasted 45 minutes standing in line and getting annoyed (seriously, 45 minutes!!!). But we had 5 meals left (my sharing went overboard) so we stopped at Starbucks (venti of course) and got coffee, fruit, baked goods, etc for the road. We would usually use a couple snacks on water bottles and a couple on treats to share, it was so hot we ran out of snacks before we ran out of meals.
Hopefully that helps someone else get their money’s worth out of it. On my last family trip we skipped most TS because the boys are done eating in 5 minutes and ready to go. We opted for the QS Dining Plan. We did go to the Garden Grill (food was fantastic) and just paid out of pocket for that. I remember the good old days with just Addie where we did character meals or table service daily.