I've had chains get badly snagged around the bottom bracket area when my front mech was wrongly adjusted. It can be a real pain around there, because it often happens under hard pedaling and can snag up very badly. You'd hardly think the pedaling would be an issue since the cahin was coming off the front sprocket, but it has been. I think its's been half off and half on when the damage was done.
If I'm going further than I'm prepared to walk, I usually carry a few tools - sometimes a lot if I'm on one of my forty mile rides that I'm doing regulalrly now. Fortunately, if you're a folder rider, you can always call a taxi to be taken home. Otherwise, if you need those tools and you haven't got them, you'll be severely inconvenienced. You can get small toolkits that weigh not much and can get out of most troubles quite easily by using them.
Multi tool - (set of hex keys, screwdrivers and chain tool)
3 good plastic tyre levers
plastic tie wraps