I use a film canister for salt when backpacking. I have had people tell me that same story about poisons leaching from the plastic into the food, but nobody is able to substantiate that. The canisters I have are labeled HDPE (high density polyethelene). Plenty of food-touching things are made from HDPE, so that by itself shouldn't be a issue. Of course wash the canister thoroughly before putting food into it.
Then there is the question of where the poison is supposed to come from. What was in these things originally was a dry roll of film.
Perhaps there is something to this as some materials are specifically rated as "food safe". I am not a chemist and don't know if there are food-safe and non-food-safe versions of HDPE. If so, then maybe there is a point to this. Since I never got a definative answer to this, I only store dry material in these canisters. That's usually the point anyway. These canisters are nicely watertight.
As for the canisters popping open, no, not really unless you are doing something very unusual. It takes a lot more than just dropping one on a hard surface to open it or hurt it. I have never had a problem with my salt canister opening or the salt getting damp, despite the outside of the canister banging around in a backpack and certainly getting wet a few times.
So I guess this answer is a long way of saying "I don't know", but I wanted to mention the issues and relay my own experience.
Back in the mid 1980s a goofball at work found a way to have some fun with a small plastic container that had a pop-off lid. I don't remember what it was, but it was about the size of a film canister or a pill bottle. He found that if you point the freeze spray (used to quickly cool electronic components for diagnostic purposes) into the container for a few seconds continuously, liquid freon would condense on the bottom. He would then put some confetti into the container and snap the lid shut. After a little while, the pressure would build up inside, the lid would pop off, and the confetti would burst out into a nice little cloud covering everything within a couple of feet.
Then someone came over with a Kodak film canister. These are rather more robust than other container he had been playing with. We figured the lid would stay on longer and allow more pressure to build up, making a bigger pop. This was tried with a thin layer of liquid freon at the bottom and worked very satisfactorily. Then of course things had to be taken to the extreme, kindof like MythBusters does when they blow something up. This time he put a good half inch of freon in the bottom and popped the lid on. We put the container lid down on a low book case in the middle of our "bullpen" area, then all stood back to the edges to see what would happen. Just as we all got back about 10 feet, the manager ambled in. He walked to the center where the book case was and idly pickup up the harmless-looking film canister. We were about to tell him to back off, but then he put it down again as idly as he had picked it up. At that point he saw us all looking at the canister and decided to back off from it too. As we were telling him what was going on, we could see the canisters swell up. Everyone kindof ducked and backed off as far as they could. It seemed like a long time, but it was probably only about 10 seconds, and the canister finally blew. It had been put back cap-down. The main part of the canister shot directly up and went so fast that it made a nice clean hole in the diffuser of the flourescent light that happened to be directly above it in the ceiling. Very impressive.
I guess the point of this story, other than to be entertaining, is how solid these canisters are. There must have been quite a bit of pressure in it before the lid popped off. I don't know how fast something of that relatively low mass has to be going to punch a nice clean hole in a plastic diffuser without otherwise cracking it, but it's got to be "pretty darn fast".