if you buy the dining plan and don't fully use it the first night, it hasn't been wasted. The entitlements (meals) that you get for the 1st night are still good until midnight of the day you check out.
So, as an example, if you get there the first night and don't use any of the meal plan, you will each have an extra snack, counter service, and table-service to use.
A good way to use an extra table-service entitlement is to make a reservation for one of the dinner shows. Hoop dee doo, Spirit of Aloha, etc. You could also use the extra table-service entitlement to make a reservation at a signature-dining experience...these tend to be more upscale dining experiences (i.e. dress nice and it's a semi-formal occasion). Since the dinner shows and signature dining each costs two table service entitlements, if you go once during your trip for dinner one night then you have used your extra table service meal.
Another way to use your extra table service meal is to go for breakfast to chef mickey's one morning, in addition to your lunch and dinner that day.
Good ways to use an extra counter-service meal would be to go get breakfast at the counter-service location at your resort and bring it back to the hotel. If you only like to eat a light breakfast, then you could go down and get as much food as you can for your one counter service, bring it back to your room and share it. Do this once for each of you, and you have breakfast for a few mornings. If you're more the midnight-snack type of family, then go and just get a counter service dinner and bring it back and share.
Extra snacks are easy to spend

Have an extra ice cream bar when you want to cool off, get a soda when you're thirsty, etc. There are a thousand ways to get rid of an extra snack. If you find that you've got a lot of snacks left over when you check out, stop by the hotel gift shop and get some packages of candy, bakery items, etc. to take home with you or eat on the trip home.
Just remember, you get the entirety of your purchased meal plan available to you at the start of your trip. and if you skip a meal, it's still available to you until midnight of the day you check out. This allows a pretty good deal of flexibility in how you use your meals.