My understanding is that in olden days honey was considered an aphrodisiac (so a doubtless popular/coarse opinion thought it a large part of the newly-weds diet) and moon means a month (more or less).
I hav'nt looked it up but I heard that it was traditional for the father of the bride to supply mead to the groom for one month after the wedding, this was known as the Honey month which became known as the honey moon as the moon cycle is roughly a month.