Line a very large sheet pan (15x21 inches) with parchment paper or foil. Lightly spray with cooking spray.
On the prepared pan, combine Rice Chex cereal, Corn Chex cereal, Golden Grahams cereal, mixed roasted and salted nuts, and sweetened coconut. Toss together with your hands.
Place unsalted butter (cut into tablespoons), sugar, and corn syrup in a pan and stir over medium-high heat until butter is melted. Bring the mixture to a boil. Boil for 2 minutes, stirring constantly. Then remove from heat and carefully add salt, vanilla (it may sputter), and optional coconut extract.
Pour the prepared sugar mixture over the cereal mixture on the pan and, using 2 wooden spoons or a spatula and a spoon, toss to evenly coat. Make sure all the cereal/nuts/coconut are well-coated. Let stand at room temperature until hardened and firm, about 1–2 hours. The mix won’t fully firm up; it is meant to be sticky and gooey.
Video
Notes
Note 1: This mixture is sticky, gooey, and very sweet. If you’d like it less sweet and/or a bit firmer, add 1 extra cup of each of the cereals. (I like this mix sticky and sweet!)Storage: Store in an airtight container at room temperature for up to 5 days. The cereal and nuts get softer/mushier each day the mix sits. I like this mix best the first or second day after it is made.