You could just say "I hope you are productive," or "be productive," or "I hope you get a lot done."
The word that came to mind, however, that hasn't been mentioned in this post is efficient.
The OED defines this as (generally referring to a machine or a system, but it can just as well apply to a resource, such as a person):
achieving maximum productivity with minimum wasted effort or expense.
For example, if I accomplished much in a short period of time, I would say I was very productive with my time because I was working efficiently.