Preheat the oven to 350 degrees F (175 degrees C).

Beat brown sugar, white sugar, and butter together with an electric mixer in a large bowl until smooth. Add 1 egg one at a time, allowing the first egg to blend into butter mixture before adding the next egg with vanilla.

Stir flour, baking soda, salt, and baking powder together in a bowl. Beat into butter mixture until just incorporated into a dough. Fold oats, crispy rice cereal, and coconut into dough; mixing just enough to evenly combine.

Drop cookie dough by teaspoonful onto baking sheets.

Bake in preheated oven until browned, 8 to 9 minutes. Cool cookies slightly on baking sheets before moving to cooling racks to cool completely.