I carry a credit card that does not charge currency conversion fees and use this ashore. It is a difference card than I use for the ship. Also carry some amount of cash depending on the length of the trip and ports being visited - only take a small amount on shore, the rest stays in my cabin safe.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014