-First, some things may be small (so sensor network security and RFID security may come to mind as a model. So achieving secrecy may be a challenge.
-Second: some things need authentication since they represent sensitive control function. How to do it?
-Some things may be in the wild, so how can one assures they are not contaminated by the adversary.
-Some things have identity and some need privacy perhaps as to not reveal too much info for tracking.
-A big new issue is that "things" may have real-world function so safety of their operation under malicious possible attack is to be considered.
I would start with possibly the literature/ software on what works in sensor networks as a possible reference point for physical security, confidentiality, and authentication issues, and with digital control networks for safety.