There are several synonyms for the phrase "come in useful". One such synonym is "prove helpful", which suggests that something has been useful in a particular situation. Another synonym is "be of use", which implies that something has been helpful in a general sense. Additionally, "come in handy" is a common phrase that means the same thing as "come in useful". Other synonyms for the phrase include "be beneficial", "serve a purpose", and "be advantageous". No matter what synonym is used, the basic meaning remains the same - something has been useful or helpful in some way.