I like to lube my chain roughly every 300 miles. If its wet or I'm near the coast, that increases in frequency.

I second using some sort of rag to wipe down the chain.

You could definitely get away with using bike shops for this in a country with lots of bike shops. Not like a slightly dry chain is critical or anything. I never carry much with me because I know any walmart, target, bike shop etc. has bike lube I can use.