I used to have a small collection of gastroliths.
That's awesome! Makes me think of one that I forgot. My son and I have a small collection of fossils and teethRocks that animals swallow to help break up food in their gut. In this case, fossilized ones. Mine were from fossil deposits containing hadrosaurs, stegosaurs, and giant sloths.
(edit: Allegedly. I got them at rock shows)