From the sources
Lot and his wife were fleeing Sdom. Hashem told them not to look back to see the destruction of Sdom. But Lot’s wife look back and turned into a pillar of salt.
How to eat it
We thought salty pretzels, you know, the sort that have the large salt crystals stuck to them, big ones that you can actually see, would be a good reminder of this story. If you don’t like pretzels, you could use potato crisps. Or serve baked potato wedges with a mound of salt next to them for dipping in.