What is the nicest thing a stranger has ever done for you?

That's very different from what I was thinking.

Most people have to be a bit selfish, to acquire greater money/power/status than others. You usually don't come in first in the race, by pausing to help another runner who fell.

A lot of the people just trying to get by, on the other hand, have it harder because of the externalities of someone else's selfishness and sometimes cheating.

But, people just barely getting by can go one of two ways: they may or may not decide to help another person who falls.

Some just getting by will think we're all in this together, and we help each other, no matter what the jerks do. I think this is actually pretty popular philosophy, and is my own thinking.

But other just getting by might think they can't afford to help others, or that it's every person for themself. That philosophy happens, too, and is unfortunate, and it can be contagious. But much of the helping-others group is resilient.

Since you mentioned NYC: A very minor anecdote, but once, when I day-tripped to NYC for a startup interview, I just missed the last train home to Boston. I went to the booth where I saw an employee, and asked them what do I do. Her initial reaction was gruff indifferent dismissal, like is a stereotype of people in NYC. (A stereotype being something like, you can't care, because there is so much misery and crazy around you, and other people's problems are just too much to deal with besides your own.) But I think she picked up on my implicit Pollyanna belief that she would help me, because, an instant later, her whole tone changed, and she projected warmth and caring, and told me how to get home on a bus. (The startup was offering me the position, but I declined, because I decided NYC was too rough for me at the time, the nice lady in the train station notwithstanding.)

I got a working visa for Japan when I was 18 (in 1999), and one night while moving from one hostel to another on the weekend, I fell asleep and missed my train stop. I woke up in the middle of nowhere. It was the last train, it was raining, I had no money on me and the banks were already closed. As I stood there under an awning two ladies asked what I was doing. I brokenly with the help of my dictionary explained the situation. They didn't understand me but flagged down a business man who spoke a little English and he called a taxi, sent it to my hostel and paid for it. It was quite expensive.

You might want to have tubes with both Presta and Schrader valves (to match the existing tube on the other tire). Theoretically you could use either, but some rims might have a hole that's only small enough for a Presta valve (so I guess that makes Presta slightly more compatible in an emergency!).

I agree that there's flexibility in the sizes. When I wanted to stock up my work's garage with spare bike tires, I got four kinds in total (basically a small Presta, a small Schrader, a large Presta, and a large Schrader). This officially covered pretty much every common road and hybrid or mountain bike with something that was officially rated or matched to it. But yes, as far as I know, one could probably get by in practice with fewer than that and use things that are officially slightly mismatched.

Specifically, I got the Specialized "Standard Schrader" 700x20-28c and 700x28-38c, and "Standard Presta" 700x20-28c and 700x28-38c tubes (the smaller ones more likely for road bikes, the larger ones more likely for mountain bikes). These are about $8 each in the U.S., so a total of about $32 for the set of four. 700c is increasingly common, although there are several other diameters that have been or are being used.

Just having a bike pump can be pretty helpful in many circumstances!

Seems like something inherently too subjective to give useful blanket advice on.

Introspection is a powerful tool though, for me anyways.

Liability goes with the owner, not the driver. If you let someone drive your car, you are liable for any damage they do.