A high key snack to me would involve 2 separate prep phases.
For instance making crackers involves making the dough then baking which makes it more of a task than cooking a bag of chicken nuggets, which is more of a wait than celery dipped in peanut butter.
I consider these the three teirs of snack making. Anything more and you have entered meal territory.
I’m not fluent, but I speak a few words of zoomer. My understanding is the post is asking for things to snack (that’s a cognate) on that is unusual or otherwise unknown
That's if you take the Boobar et al. (2022) interpretation. Under Chumbawumba's Theory of Language, a "low key" refers to an easily accessible doorway in which things pass, as opposed to a "high key" in which one must be on their tippy toes.