Daenerys stunt double Rosie Mac poses with her fellow stand-ins
Much like the Force in Star Wars, Gaffer Tape has a light side and a dark side, and it binds the universe together. Gaffer Tape, not to be confused with Duct Tape, is a heavy cloth pressure sensitive tape. The adhesive is rubber based, which makes it more resistant to heat, and much easier to remove from the surface it has been applied to. And once you see it used on set, you'll be amazed how many applications it's used for! Again, not to be confused with Duct Tape - which is great, in some circles, isn't nearly as awesome as Gaffer Tape!
Gaffer tape is used by all departments, even though it's named for the head electrician. Camera, grip, production, even make-up and wardrobe use gaffer tape! Common uses are to secure cables to prevent tripping or to hide cables from the camera, a quick label maker, to mark focus points or ‘spikes’ noted for talent blocking, holding props or paper, and of course to repair broken things. There are as many colors of gaffer tape as colors in the world, but the most common is matte black, as it tends to not reflect light.
The Apple Box, as it's known in the grip department is an extremely versatile tool used in film and television set production. It's a wooden box, with handles, and comes in a variety of sizes.
The large size, or Full Apple, is uniformly 20" x 12" x 8". The size and term come from the old-fashioned produce crate that you might find at a grocery store, apple orchard or your favorite farmer's market.
The next size is a Half Apple (20" x 12" x 4"), then Quarter Apple (20" x 12" x 2") and then the Pancake or Eighth Apple (20" x 12" x 2").
These sturdy boxes are used for propping up items, often temporarily, and even as chairs or lifting stands for actors and also crew. Sometimes they're needed to help elevate dolly tracks or actors. Sometimes they are referred to as "man makers", but often not in front of actors who are shorter than their leading ladies.
There are also Mini Apple Boxes, which are 10" in length rather than 20", and sometimes you'll find a grip department that uses nesting Apple Boxes as well, but their structural integrity isn't nearly as strong.
To read more, Sources: Uva, Michael. The Grip Book (Fourth ed.)