"Summertime" seems one of those songs that is regarded as fair game by many singers, regardless of experience. Personally, I think it is very difficult to sing well, and I am, normally, wishing I was somewhere else when it is being sung.
"Chicken on a Raft", however, is a great participation song, one that can really take off with a bunch of enthusiastic chorus singers. It is probably, or was probably, sung too often in the UK, and its very popularity has made it unwelcome in some quarters, sadly.