Preheat and prep: Heat the oven to 375°F (190°C). Line a mini muffin pan with paper liners or lightly grease it.
Combine dry ingredients: In a large bowl, whisk the flours, oats, sugar, baking powder, baking soda, salt, and cinnamon.
Mix wet ingredients: In a separate bowl, whisk eggs, milk, yogurt or applesauce, oil, vanilla, and mashed banana until smooth.
Bring it together: Pour the wet mixture into the dry ingredients. Stir gently until just combined. Do not overmix; a few small lumps are fine.
Fold in mix-ins: Add your chosen mix-ins and fold lightly.
If using berries, toss them with a teaspoon of flour first to help prevent sinking.
Fill the pan: Spoon the batter into the mini muffin cups, filling each about 3/4 full.
Bake: Bake for 10–12 minutes, or until the tops are set and a toothpick comes out clean. Rotate the pan halfway through for even baking.
Cool completely: Let the muffins cool in the pan for 5 minutes, then transfer to a rack to cool fully. Cooling prevents condensation in snack packs.
Assemble snack packs: Add 2–4 mini muffins to each container. Pair with extras like cheese cubes, sliced cucumbers, or a small fruit leather if desired.