Photography is expensive. When PJs first start, it's really expensive.
One of the cheapest and most useful items a film-based PJ can carry in the bag or vest is a film puller. It's a tiny set of two thin spring-steel leaves. It allows PJs to grab film inside the canister and pull it back out. They cost about $5. If the PJ saves only one accidentally rewound roll of film, it pays for itself.
What a film puller does
Film pullers allow PJs to change film speeds during assignments while only killing a frame or two on the roll. Although this isn't the best way to accomplish changing speeds, it works.
If a PJ shoots 10 frames on a 36 exposure roll of 100ISO film, then s/he needs to go indoors to complete the shoot, it causes a problem. Either the PJ needs to rewind the film and lose the other 26 frames (but still pays the same to have it developed [in chemistry or lab fees]) or use a different camera body indoors. Nobody trots around with nine different camera bodies, so frames get wasted.
However, if the PJ has a film puller, s/he can rewind the film, mark the number of frames shot, and come back to finish the roll later. It's important to mentally note the frame number before rewinding the film. It's equally important to store partially exposed rolls of film separate from unexposed film (to avoid accidental double exposures).
When PJs are back to a same-speed environment (light level), use the film puller to recover the film tab. Load the camera with the already exposed film. Set the camera to manual at the highest shutter speed and stop down the aperture (f/22ish). Cover the lens with a lens cap, coat or hand and fire the same number of frames plus one more for insurance. Depending on the type of camera, there should only be one or two dead frames. Point-and-shoot folks need to completely block light from the lens because the flash will probably fire.
Additionally, PJs who process their own film have a much easier time if they square the film before going into the loading room. It's impossible to machine process without having the tab pulled, but you don't initially need the film-pulling machine professionals use (BTW, a $5 puller often works better).
Art photographers and PJs working on illustrations can deliberately double expose film with the help of a film puller. If the camera doesn't have a shutter reset and the camera has a stable loading pattern, the artist can place multiple elements on the same frame by reloading the film.
How to use a film puller
With the film inside the canister, rotate the spool to tighten the film. When it's tight, there's an audible click each time the film tab passes the exit slot. PJs need the film tight to insert the puller and grab the film.
Place the leaves of the puller in the back position with the ends even. Insert the puller inside the film slot of the canister. Pull the bottom leaf back while letting the top leaf remain fully inserted. Place the film against your ear and rotate the tightly wound spool slowly. As soon as it clicks, stop turning. Slide the other leaf forward inside the canister.
At this point, the film is between the two metal leaves. Bend the puller against the outside lip of the film exit slot to put pressure on the film. Quickly yank the puller out of the canister. The film tab should come out with the puller. If it doesn't repeat the steps listed.
Enough for now,