Now I assume hope you regularly research prices of flights and hotels before booking, but what about activities? Along with the added perk of looking for reviews on whether a particular stop is a tourist trap or worth the money, you can also save money booking "big ticket" items. Museums, theme parks, and other destinations often offer discounts for activities prebooked online because so many people don't do this and are willing to shell out more cash at the door.
Don't be this person, and thoroughly research your destination and activities. In addition to checking out the tourism board, my favorite place to stop is the website of the local paper or city magazine. Periodicals geared toward locals usually have reviews of newer places and upcoming events, sometimes even discounts, too!