It could be contrasted with a "heavy snack," which would be something more filling and substantial, like a sandwich or a burger.
However, if you're looking for a similar idiom, here are some options:
* A bite to eat: This idiom means a small amount of food, typically consumed quickly.
* A nibble: Similar to "a bite to eat," this idiom refers to a very small amount of food.
* A quick snack: This phrase emphasizes that the snack is consumed quickly and without much effort.
These idioms all convey the idea of a small and simple food item, similar to what "light snack" describes.