I'd hit up the beach and go brunch-hopping before getting the real food (re: babi guling). If I still have time, I've always loved hanging around Ubud for the cooler ambiance for exploring on foot! And I would end the day with a nice seafood grill somewhere in Jimbaran.
I remembered the first time I snorkled in Menjangan. Over corals and trenches, the water was super clear and I could even chase a school of fish. The water was warm and our guide caught a few little fishes to be grilled by campfire. It's definitely a memorable trip.
Don't miss out on a good plate of Nasi Campur. It's cheap, hearty, and more often than not, vegetarian friendly! Try asking for Nasi Kuning if available (turmeric rice).











