IMPROVISE

[verb] - to invent (something such as a speech or a device) at the time when it is needed without already having planned it, or (of actors or musicians) to perform without fixed speech or music, making it up as it is performedI hadn't prepared a speech so I suddenly had to improvise. [I]During certain scenes of the play there isn't any script and the actors just improvise the dialogue. [T]We didn't have anything to sleep on so we had to improvise a mattress from a pile of blankets. [T]The band improvised on 'When the saints go marching in'.We lay on the beach, sheltered by an improvised windbreak.