It's been a few years, but we did an average of my courses and the bunker count was...a resounding 21 average per course! I have always believed that most courses are over-bunkered. There are so many wonderful "surprise" "hazards" that do not involve sand and a more complicated drainage infrastructure.
Trees, as mentioned, can be great — although I found out early in my career that they die occasionally
Here is one that we took great care with, and 20 years later it was gone:
Some other "hazards" Swales, bumps, counter-slopes, hollows, sleeper walls, ditches, rock outcrops and waste areas.