Give your child large containers of several different snack items they like (dried fruit, nuts if they're old enough to eat them, cereal, etc.). Give them a measuring scoop and let them scoop some of each item into a big empty container and mix it up. If you like, make this available to them on a shelf they can reach so they can get their own snack. For an older child, you can write a simple recipe (e.g., 2 scoops of cereal, 1 scoop of cashews, etc.) to make it more challenging.