In regards picking things up off the floor... I don't think it's a social requirement, but I think it's a nice thing to do. Whether it's reasonable depends on what the item is, whether you know where it goes and whether it's close, and it can also depend on what kind of item it is and whether getting dirty is an issue. Customers can't wash their hands as easily as staff can. Also, would you want a customer picking up, say, a nectarine, and putting it back on top of the others? It's probably bruised because it fell, but the bruise may not show immediately. Another customer would pick it up without knowing that it fell on the floor.
I try to, in other circumstances, pick/clean things up. In fact, the city we used to live in actually had signs asking people to pick up 5 pieces of trash. Perhaps because of the signs, I rarely saw that much trash.
But I do try to pick up trash, clean out the paintbrushes/paint left on the counter at the play place, etc.