GeneO 

I carry a spare and patch kit and CO2 inflator, chain tool and links + etc. It really isn't much to carry - can all easily fit into a micro seat bag. Never been stranded except when I had some BB issue.

I ride trails a lot so if I see someone who is having some mechanical difficulty I always ask if they are good or need anything. I actually never have gotten taken up on the offer that I can recollect.

loky1179

I always yell out "Are you OK? Do you need help?".

Then, when they answer either yes or no, I can respond "Great to hear!" and keep riding.

Astrozombie

Yell "That's why you carry a spare tube, haaahaaaaa (In Nelson voice)"

thumpism 

This is very important. I was riding with my girlfriend to visit her parents an hour away and we came across a young guy who'd badly bent a wheel on his third day out on a cross-country ride. I had no tools but the knowledge. This guy was a novice but had listened when someone suggested which tools and spares he should carry with him. We gave him a lift to the parents' place where I could work in leisure (and shade) using his tools to straighten his wheel and get him going again. He was about 30 miles from the nearest shop, so he might have learned a hard lesson had no one stopped.

As a rule I ask, but once had a very strange experience riding home from a night class. Guy was carrying the bike slung over one shoulder and the front wheel in the other hand. When I asked if he needed help he yelled and cursed at me. He was obviously upset in general and pissed at me in particular so I rode on, but it occurred to me later it was a great way for him to steal a bike.