In your largest bowl, or a large roasting pan, mix all ingredients except the M&M's, sprinkles, and candy melts. Do not over fill your dish, you will need room to toss the ingredients together.
Melt white candy melts (or white chocolate) in a microwave safe dish (at 50% power) in 30 second intervals until almost melted. Stir until completely melted and smooth. Pour the melted chocolate over the dish of snacks and then stir, stir, stir! It's up to you if you want the mix to be totally coated, or lightly coated (depending on the amount of melted chocolate you use).
When the snacks are evenly coated, pour entire mixture out onto a baking sheet (or two if needed).
Immediately (while the coating is still warm and melty) add sprinkles and M&M's. They will stick to some of the clusters as the white chocolate cools (this is a good thing).
If desired, melt another color of candy melts (in this case, I used pink), and drizzle the colored candy melts over the snack mix as it cools. This will add a bit more color.
Allow snack mix to cool and chocolate (and candy melts) to set up (about 30 minutes). Once cool, break apart as needed and store in an airtight bag or container.
Party mix with popcorn in it will remain fresh tasting about 2-3 days, and a bit longer without popcorn.