One or 2 original songs if they are good enough and are well received. The songwriters will usually want to play more and believe their songs are better than they actually are which can cause tensions.
In one band we played 1 original song which was well received and left it at that. In my current band the singer and guitarist wrote a song years ago. it comprises 2 chords and is very linear and doesn't go anywhere. They hsve talked about bringing it into the set and would if they could. I told them the song is stinky poo and no way would I play it. Their inflated egos needed puncturing.