Gaffer tape isn’t just one of the most essential tools in a filmmaker’s gear bag, it’s also one of the most versatile. Gaffer’s tape can be lifesaver!
1) Marking spots, such as where your actor will stand, where props should be and where you need to put your tripod if you want to match up the perspective you had in your last shot.
2) Laying/securing cable
3) Fixing broken and hanging stuff
4) Mounting gels to lights
5) Labeling stuff especially your memory card. (prevent others people from using or formating it)