Step 2: Reload That Instamatic
Get a roll of regular 135 film. Usually 100 or 200 speed is best for Instamatic cameras.
Now you need a totally dark place to reload the old cartridge with fresh 135 film. Like a photo darkroom, or a closet or windowless room with a rolled towel over the door crack. Or use a film changing bag.
You can make your own film changing bag with heavy-duty black garbage bags. Just triple-bag on a table, dump in your stuff, and stick your arms in. Put a heavy coat on top to keep the bags closed.
Wash and dry your hands thoroughly before handling the film to keep fingerprints off.
Tape the loose end of the 135 film to the 126 spool.
Tape the Instamatic cartridge film window and ends gently closed with black tape.
Put a piece of black tape over the window in the camera back.
Place the film, taped cartridge, scissors and camera into the changing bag.
In the dark, slowly pull the film out of the 135 canister and cut it loose with blunt scissors.
Wrap the loose end of the film around your finger the way it naturally wants to curl.
Coil it up tightly, holding it by the edges as much as possible to avoid fingerprints.
Place the coiled film and the spool into the 126 plastic cartridge.
Now load the 126 cartridge into the camera in the dark and shut the camera back.