"Make up as goes along" is a common phrase used to describe someone who is improvising or creating something on the spot. However, there are many synonyms that can be used to convey the same concept. Some examples of alternative phrases include "winging it," "flying by the seat of one's pants," "going with the flow," "ad-libbing," "playing it by ear," "spontaneous," and "on the spot." All of these phrases suggest that someone is creating something without a set plan or previous preparation, and instead relying on their own creativity and ingenuity.