This should really go without saying, but always have a flashlight with you. One never knows when your need one even during the day! Lots of places have nooks and crawlspaces without lights – not to mention the “standard” night investigation where being able to see is a must. Remember to use a red lens’ on your lights to keep your night vision intact during dark/night investigations as bright lights in the dark can blind you or other investigators. And always test/change batteries before an investigation!