Prep your half sheet pan by greasing it well with butter. Preheat the oven to 250 degrees.

In a large mixing bowl, combine the three cereals and pecans and mix well. Add in other ingredients you like, such as pretzels, coconut, or a different type of nut.

Over medium heat, melt the butter and brown sugar and bring to a boil, stirring constantly. Remove from heat and add the salt and vanilla, and mix well.

Slowly pour it over the cereal mixture, then stir until everything is well coated.

Spread the coated mixture evenly on the half sheet pan. Bake for 60 minutes, stirring every 15 minutes.

Remove from oven and let cool completely.