Mix cereals, nuts and pretzels together. Add oil and toss. Add spices and toss again. Bake at 250 degrees for two hours. Toss every 15 minutes.
The secret is to use a HUGE pan - ours was sold as a sweet corn cooker. It almost fills the oven with only the bottom shelf in place. You want the HUGE pan so you can have enough room to toss the mixture instead of stirring it. That way you don't smash the cereal so much.
If you have a Sam's Club (or something comparable) nearby, they often sell the three Chex cereals in a combo pack, just the right amount of each (or close enough). They also sell a 2 1/2 or three pound container of nuts. And a 48 oz barrel of pretzels. Thus, the actual amounts vary, depending on the size of the containers, and that seems to vary from year to year. Trust me. It'll come out just fine! Serving size is just a guess.