Here in Maryland, the way used to cover personal property not identifiable as being in the trust is a "pour-over will." Basically, it says "anything not in the trust goes into the trust."

I have never heard or seen of a trust clause that automatically puts purchases in the trust, but every state has different rules. Some states, like Maryland, allow a trust to be set up "in perpetuity," that is, it can exist forever (with some restrictions that the trust must comply with). Other states adhere to the more traditional common law rule, basically limiting the trust to approximately 120 years.