1. Preheat oven to 350 degrees F (175 degrees C).
2. 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 to blend into the butter mixture before adding the next with the vanilla.
3. Stir flour, baking soda, salt, and baking powder together in a bowl. Beat into the butter mixture until just incorporated into a dough. Fold oats, crispy rice cereal, and coconut into the dough; mixing just enough to evenly combine.
4. Drop cookie dough by teaspoonful onto baking sheets.
5. Bake in preheated oven until browned, 8 to 9 minutes. Cool cookies slightly on baking sheets before moving to cooling racks to cool completely.
