Preheat the oven: Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone baking mats.
Cream the butter and sugars: In a large bowl, cream together the softened butter, brown sugar, and granulated sugar using a hand mixer or stand mixer until light and fluffy (about 2-3 minutes).
Add eggs and vanilla: Add the eggs, one at a time, mixing well after each addition. Then add the vanilla extract and mix until fully incorporated.
Mix the dry ingredients: In a separate bowl, whisk together the flour, baking soda, and salt.
Combine: Gradually add the dry ingredients to the wet ingredients, mixing until combined. Stir in the oats, chocolate chips, coconut, nuts, and M&Ms (if using) until everything is evenly distributed.
Scoop the dough: Using a tablespoon or cookie scoop, drop heaping spoonfuls of dough onto the prepared baking sheets, spacing them about 2 inches apart.
Bake: Bake for 10-12 minutes, or until the edges are golden and the centers are set. They will firm up as they cool, so don’t worry if they seem a bit soft right out of the oven!
Cool: Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.