Place corn syrup and sugar into 3-quart saucepan.
Cook over medium heat, stirring frequently, until sugar dissolves and mixture starts to boil. DO NOT keep boiling, it will make the mixture around the rice krispies hard to cut into and also make the rice krispies too crunchy. Remove mixture from heat. Stir in peanut butter. Mix well.
Add KELLOGG'S® RICE KRISPIES® cereal. Stir until well coated. Press mixture into 13 x 9 x 2-inch pan coated with cooking spray. Set aside.
Chocolate-Peanut Butter/Butterscotch Layer
In a microwavable bowl, microwave the chocolate chips and peanut butter or butterscotch chips together in 20-30 second intervals stirring in between each interval. (A minute and a half is what it is usually is for my microwave.)
Pour and spread evenly on rice krispie layer.
Sprinkle pretzels, mini Reese's Pieces, peanut butter or butterscotch chips and several grinds of sea salt on top of chocolate, if desired.
Let cool completely before cutting into squares.