Ditto to the responses Kevin and Terry made. We use Wilbert urn vaults; some of our cemeteries require urn vaults while others do not. When presenting the urn vaults during arrangements, I always offer the family can place small, meaningful items in the vault with the urn. We do this in a ceremonious manner at the convlusion of the graveside service. People embrace this, so most of my families elect to use an urn vault even when one isn't required.
As for items placed in the vault, they are typically letters from family members, tobacco, cards, fishing lures, hobby items, and folded clothes.