In sit down restaurants, I will leave 15% for average service and adjust up or down accordingly. For takeout and other reduced service situations, I will usually tip a dollar or two depending on the total. I will tip pizza delivery and things like that.
I went on one cruise and at the end we were told to attend a mandatory pre-disembark meeting where they did nothing but tell us why we needed to leave a very large, insinuating several hundred dollars, for the crew. I was so offended by this that I left them nothing. Wouldn't go back to that cruise line either. After the cruise they also started calling me trying to get me to take another one. I told them what I thought of the first one and got removed from that list.