Melt the butter.
In a very large microwave safe bowl add the melted butter, brown sugar and the white corn syrup. Give them a stir.
Microwave 2 minutes on high. Stir and microwave on high for 2 minutes and stir.
Add the vanilla and the baking soda. Stir together. It will get foamy.
Measure and add in the cereals, pretzels, and cheese crackers. Gently toss to coat as best you can. Don't worry if it is not coated evenly.
Microwave on high for 1 ½ minutes. Gently toss to coat the cereal and crackers. Repeat this step and microwave on high for 1 ½ minutes. Gently toss to coat the cereal and crackers. Then again for 15 seconds. Gently toss.
Place a large sheet of parchment paper, waxed paper, or a large baking sheet. Place the snack mix on that to cool. Once cooled gently break it up and store in an airtight bowl or bag.