There's a difference between a snack you hand to a child and a snack they made. The first one gets eaten, usually. The second one gets eaten proudly, and the cook starts looking for the next thing they're allowed to do alone.
None of these require a stove. A butter knife, a bowl, and a spot at the counter are enough. Your job is to keep the ingredients somewhere reachable and then stay out of the way.
1. Yogurt bowl. Plain yogurt, and a small station of toppings: berries, granola, banana coins. The child assembles. The topping station is the point; assembling is the fun part.
2. Rye bread with cheese and cucumber. Spreading butter badly is a rite of passage. The slices will be crooked. Serve them anyway.
3. Fruit plate. Give them a real (small) knife and a banana, some strawberries, a peeled orange. Cutting soft fruit is safe early knife practice, and a plate they arranged themselves gets finished more often than one that appears in front of them.
4. Crispbread stack. Crispbread, cream cheese, a slice of tomato or ham. Three moves, zero risk, looks like real cooking.
5. Smoothie, supervised. They load the blender: banana, frozen berries, milk or yogurt. You press the button, or they do, with your hand hovering. Loud, slightly messy, extremely popular.
6. Vegetable sticks and dip. The trick is letting the child mix the dip: yogurt, a squeeze of lemon, herbs. Vegetables that come with a dip you made yourself are a different product than plain carrots.
7. Boiled eggs, peeled by the expert. Boil a few eggs in the morning and leave them in the fridge. Peeling an egg is oddly satisfying work, and a peeled egg with a little salt is a complete snack.
8. Overnight oats. Oats, milk, a spoon of jam, into a jar, into the fridge. The child preps it in the evening and finds their own breakfast-snack waiting the next day. Delayed gratification with a lid on it.
9. Popcorn from the pot. This one needs an adult at the stove, but the child measures the kernels and does the shaking-the-bowl part. Popcorn is corn; as snacks go you can do far worse.
10. The snack plate they invent. Once a child has done a few of these, hand over a plate and the fridge and ask for their version. Some combinations will be strange. Eat them with a straight face.
Why bother?
The same reason we build anything else around ownership: a child who makes their own snack is practicing the skill of looking after themselves, one butter knife at a time. Things get done when they're yours to do.