I've had a film jam before - it always leaves a nasty taste. I much prefer the blueberry or rasberry varieties.
A friendly tip from me: before loading new film into a holder, always open the holder half a centimetre or so and check that the holder is indeed empty. If you pull the slide all the way out in one go, you won't be able to salvage anything from the well exposed sheet already residing in the holder .....
Loaded holders reside in my fridge untill I leave for photographing.
I just have to remember to take a few cans of beer along, so I don't forget to take out the holders