IMHO, what I paid for the items brought or what additional fee is added is not relevant. I tip according to what was brought. A couple of sodas and cookies, a buck or two. A big tray of breakfast items, maybe five bucks. A couple of bar drinks maybe two dollars.
I'ld Rather Be Cruisin'
Disney Magic February 4 2006
RCCL Freedom January 20 2008
Disney Wonder October 2009
RCCL Rhapsody of the Seas September 2011
Disney Magic February 2012
Disney Wonder January 2014
Disney Wonder to Hawaii 2015...I hope!