On Carnival excursions, tips for excursions are NOT included in the excursion fare. This is from the FAQ:
Frequently Asked Questions
Should I tip the tour guide?
Tipping is a discretionary matter. However, it is customary around the world, if you are pleased with their excursion, to tip the tour guide. A general rule of thumb is one dollar per person for a half-day excursion and two dollars per person for a full-day excursion.