pick-and-mixˌpick-and-ˈmix adjective British English 
if something is pick-and-mix, you are free to choose the things or parts that you want and not choose the rest: 
Students can select parts of the course on a pick-and-mix basis.
if something is pick-and-mix, you are free to choose the things or parts that you want and not choose the rest: Students can select parts of the course on a pick-and-mix basis.