For conversational manner I guess that please, thank you, you're welcome, etc are good for a kid to learn.
People here do ask "How are you?" and the common answer is to say "Fine thank-you, How are you?" It is like saying hello.
I try to teach my DD to say Hello back when friends or aquantances say hello to her. She is 4 and more often than not she just stares at them.
For manners, I would like my children to wait their turn to walk through a door, onto the subway or bus, etc. Learn to walk on the sidewalk in order to allow other people their space, etc.
Eventually, I would like them to hold doors for people, give up a seat on the bus for an elderly person, small child, pregnant woman, person with a lot of bags, etc.
I would hope that they would grow up to be the kind of person to help a woman lift her stroller onto the bus. Or help a person lug their grocery cart down the stairs to the subway. Or any of the other common instances of seeing strangers struggling with something and help.
Social skills. I would like my children to learn how to sincerely be interested in friends. Ask them questions and listen to the answers. Wait their turns in conversations to have the conversation flow and such.
I hope my children would have enough manners to not do things like talk loudly on their cell phones or with friends in public spaces. basically be aware that it is a public space and they are sharing it with others who have a right to enjoy the space too.
I also hope that they have enough manners to not do things like talk on the phone while also being serviced at any type of check out or cashier. It is my pet peeve when people do things like talk on the phone while they are in line, order their coffee/food/whatever, pay and everything while still on the phone in conversation. I feel it is rude to the service provider and dehumanizes them.
Basically I guess I want my children to have enough manners to know that they are not the only people around and treat others as members of their community who deserve respect.