Preheat the oven to 375 degrees F (190 degrees C).
Mix sugar, peanut butter, butter, water, vanilla, and eggs together in a very large bowl until smooth.
Combine flour, baking soda, and salt; stir into cookie batter. Mix in oats and raisins, then carefully stir in cereal.
Drop 1/2 cupfuls of dough onto ungreased cookie sheets, spacing cookies about 4 inches apart. Flatten cookies to 1 inch thick.
Bake in the preheated oven until cookies are lightly browned at the edges, about 10 to 12 minutes. Let stand on the cookie sheets for 5 minutes before removing to wire racks to cool completely. Store at room temperature.