It's situation dependent.
Making out, with groping, is not appropriate most places. A tongue war isn't the best idea in public, but it depends. A festival is a different atmosphere than a shopping mall.
I disagree that kissing isn't always appropriate at funerals. It depends on the kiss. Some people of many cultures kiss to greet each other. It can also be an action of comfort and solidarity. It depends on your culture, your relationship, and the intent behind it. If my SO kissed me at a funeral, it would not be a sexual kiss, it would be a sign of comfort and affection, and I really don't think anyone would find it inappropriate, because it would obviously not be sexual in intent.
It's about being respectful to those around you.