Ideally, you're looking for something that spikes blood sugar fast (i.e. high glycemic index). This is why e.g. Skittles/Sour Patch Kids/fruit snacks (mainly the kind that don't... actually have any fruit, lol) are a go-to for type 1s.

You're basically looking for something that's analogous: as crack is to cocaine, <low snack> is to sugar. Hits fast and doesn't last as long.