If you'll be frequenting the same areas regularly, and the same restaurants, select a few items that you know are filling and healthy, or reasonably healthy, and stick with those staples, rather than letting the unhealthy goodies from the menu tempt you each time.
Check out the restaurant's menu on their website in advance if you can, and know what you are going to order before you arrive.
Find restaurants within walking distance of your hotel and walk, rather than drive to the restaurants.