I've removed stuff in the open at weddings shooting with medium format and no mag back, when I was young and daft and didn't know any better, with no probs.
As long as the roll is kept wound tight though you should be OK - the backing paper is wider than the film. Why take the risk though, you can't be too careful. I'd always load or unload any film in subdued light, or at least turn with my back to the sun in a situation where I had to do it there and then.
Once it's sealed, some sort of wrapping to make sure, doesn't go amiss - the tin foil tip was a good one.
I never trust the light traps on 35mm film cannisters anyway - even with the film leader left out, so I'd always seal those in something too.