Preheat oven to 350°. Line a 15x10x1-in. baking pan with foil; grease foil. Arrange Saltines in a single layer on foil.
In a large heavy saucepan, melt butter over medium heat. Stir in brown sugar. Bring to a boil; cook and stir until sugar is dissolved, 2-3 minutes. Remove from heat; stir in vanilla. Spread evenly over crackers.
Bake until bubbly, 8-10 minutes. Immediately sprinkle with chocolate chips. Allow chips to soften 2 minutes, then spread over top. Sprinkle with peanuts, pretzels and M&M's minis; shake pan to settle toppings into chocolate. Cool.
Refrigerate, uncovered, 1 hour or until set. Break into pieces. Store in an airtight container.