I have always been wondering: why do we find small non-eatable items while searching the bodies of some animals? For example, I often find money, spoons or forks inside rats and mudcrabs. What is this supposed to mean? That they ate somebody who carried these items?

Yes, pretty much that they either ate the item or ate some or something that carried or ate that item.

Or in some cases, like with Ogres, they may have found the item and are carrying it around.

Some animals are attracted to shiny items and will eat or hoard them.