This might be better coming from someone more senior than myself but I think I’ve seen a few posts that have suggested this when one of us fears being “pigeon-holed”
To keep yourself diverse then you could design different products in your spare time to show you have the ability to apply the design process to all aspects of ID. Granted it will never be something that is put in to production but if you can clearly showcase good development from idea, research, concepts and to execution then any future employer not in the packaging world how you handle a project. Challenge yourself in designing an innovative kitchen product, a game changing consumer electronic etc etc.
But I have to say PackageID’s advice is pretty solid and sounds like a really good way to progress up the career ladder, as well as being incredibly interesting. Also, places like Unilever etc have silly money to spend so you could be guaranteed a hefty pay packet. Believe me, I have friends in places like that and they earn far more than my friends in consultancies…