If you're not yet familiar with this useful product then I'm here to make sure you will. As far as I'm concerned, gaffer is a must have in a photographer's bag. I've been using it for so many tasks that I can't list them all. You can use it to attach a backdrop to a wall when you're out of the studio and have no stands, you can must use it to secure cables to the floor, like extension cords, sync cords, laptop AC supply etc...
Needless to say when your cables are loose on the floor - or even worse- hanging in the air, people could trip over them and fall or they could just collapse and destroy your gear. So this is also when gaff tape proves so useful.
I like to carry one black and one white gaffer tape roll and then use the appropriate color to make it blend in. For example if I want to secure cables to a black stand I will use the black roll, and if I need to hang a white backdrop I use the white one. This way I don't get unwanted black stripes in my frame.
Tip: Don't leave gaffer attached to a wall for too long. Remove it as soon as you're done shooting. Gaffer tape that is left attached to a wall for few days can peel some paint as you attempt to remove it.