Position rack in the center of your oven. Preheat to 225 F. Line a large rimmed baking sheet with a silicone baking mat.**
In a large mixing bowl, combine cereal, nuts, Saltines, and pretzels. Set aside.
Place a large saucepan over medium heat, and melt the butter.***
Once the butter has melted, stir in the brown sugar, corn syrup, and salt.
Bring the mixture to a boil, stirring frequently.
Allow the mixture to boil for 2 minutes, and then remove from the heat.
Whisk in vanilla extract, and then add the baking soda, mixing well. The toffee will foam. Continue whisking until well-combined.
Pour the hot toffee over the cereal mixture, and carefully fold to coat the cereal mixture with the toffee mixture. The cereal mixture doesn't have to be perfectly coated.
Spread the cereal mixture in an even layer on the prepared baking sheet.
Bake 15 minutes.
Carefully stir the cereal to coat with melted toffee.
Continue baking for 15 minutes, stir, and then bake for another 10-15 minutes.
Remove from oven, and then toss one more time.
Spread into an even layer, and let cool.
Break into pieces to serve.
*You can swap in an extra cup of cereal, crackers, or pretzels in place of the nuts. **I use a half sheet pan. If you don't have a baking sheet that's that large, use two smaller baking sheets. ***You'll need a pan that will give you enough space for the toffee to foam up when you add the baking soda. ***Nutrition values are estimates.