Hello Katrina! You're going to love the variety and convenience of having the Disney Dining Plan. Although there is no official list of locations where you can use your snack credits, you won't have to search very far! Most Quick-Service restaurants, outdoor food carts and select merchandise locations all have items which qualify as a snack. You will need to look for the purple and white DDP symbol next to the food item on the menu boards. A snack is considered to be a single-serve item that is under $4 before tax. It must be edible, non-alcoholic, non-merchandise, and non-souvenir. While I can't confirm if you would be able to get an ice-cream cone, you can definitely use the snack credits at the carts selling frozen novelties stationed throughout the parks. Other items would be a single-serve box of popcorn, some bakery items, single-serve bag of chips, bottled water, soft drinks, powerade, juice or milk. etc. Best advice is to just look for the logo.
Here is a link for the current
2013 Disney Dining Plan, which has an explanation of where and how you may use each type of credit on the plan. I hope you find this information helpful.
Please let me know Katrina, if you have any other questions while planning your trip. Have a magical day!
Kristen