If I had to pick the perfect snack, I'd vote for edamame. I LOVE edamame and could eat it every day. I think edamame is the perfect snack because it's got a nice substance to it, it's a vegetable (soy bean), it's easy to eat, and 1/2 a cup is 150 calories has 4g of fiber, and 12g of protein.
I love edamame in the shell or unshelled. I love it best unshelled, slightly warm and sprinkled with sea salt. I also like to sprinkle on Seaweed Gomasio (Sesame seeds, seaweed, salt), or a wee smidgen of cayenne pepper. Trader Joe's has chocolate covered edamame and it's different, not bad. I think I like the edamame though bare and beautiful. Simple.
Typically, you'll find a bag of Woodstock Farms Organic frozen edamame in my fridge. If you have to have a midnight snack, edamame is a better choice over the cookies or cheese and crackers. I would bring edamame to snack on after a long run when I was marathon training because it's a nice way to get some protein for your muscles after long mileage.
In fact, as I type this post there is a small bowl of edamame sitting next to my laptop :)