The last time I stopped to help a stranded cyclist, I sure got into more than I planned on, but it all worked out OK. A man, riding with his 12 year old daughter was on the side of the trail, looking like he had tried in vain for a long time to sort out a mechanical issue, and had given up. He was a long way from home, and had no one he could call to come and get him.
The issue was the chain jammed between the chain rings and bottom bracket, and I mean, twisted around, jammed in there tight. It was a newer, mid level full suspension mountain bike, so I didn't want to get too forceful with it as paint damage was likely.
Another cyclist, (a roadie) stopped almost at the same time as I did, and we kind of worked as a team to sort it out. The guy with the jammed chain was not equipped or knowledgeable in mechanical matters, but the other guy had a good assortment of tools, and I had my multi tool, so we went to work.
The one tool we really needed, neither of us had. The crank had a self extractor, and a 8mm hex key would have pulled the crank right off, and freed the chain.
But we were equipped to remove the chain rings from the crank, so that's what we did.
Freed the chain, inspected it for damage, put everything back together and got him on his way.
I didn't have my phone with me, and I was gone longer than I thought. My wife was going nuts worrying about where I was.
I often ride without my phone, but since then, I try to remember to grab it before I go out the door.