It is rare if you can get the film with a perfect 2nd exposure right over the 1st.
I have a point and shoot Olympus Infinity II, which automatically winds in the film for you. I love that when the roll is done it winds it right back.
The magic of this camera is that it leaves the small tab of film out of the container. This allows you to safely remove the film from the camera without any exposures, and then load it into another camera. As you may know... rolling film back into its container is hard to gauge, and once it is all rolled in...that's it...unless you want to risk going into the dark and dissect and reassemble the roll.
My next venture for photography...
Take a full roll of film on the Olympus Infinity II...
Then reload into a camera that has a masking capability, such as a Fisheye, or Panorama.
This way the masked areas will show case the original photo, while the unmasked area will showcase the secondly exposed photo.
A fellow photographer of mine, Traci McMillan seems to have got it down pat. Look at the amazing double exposed photos she created.
Cheers!