Be sure to check with both the post office and sanitation department before gifting to these two hard working groups. Sometimes they are not allowed to accept gifts.
You could try quotegarden.com for some poetry etc if that would help. but I agree with KansasCindy, just say it from your heart. Your own words are always the best. Something like: Thank you for all you do, I appreciate it greatly, Have a happy holiday season and thanks again.