Prepare popcorn according to package directions; remove unpopped kernels. Combine popcorn and peanuts in a large roasting pan; set aside.
In large saucepan, combine sugar, butter, water and salt over medium heat. Stir occasionally until bubbly around edges. Cook 2 minutes, stirring occasionally.
Remove from heat; stir in baking soda and vanilla. Pour over popcorn; stir until well coated.
Bake in a preheated 300°F oven 15 minutes, stirring halfway through. Remove from oven and spread on greased wax paper. Quickly separate; let cool. Store in an airtight container.