How do i keep cut flowers fresh besides adding flower food in the vase?

Put a sprinkle of salt into the water every time you change it (at least every other day). The salt fights bacteria that makes flowers fade fast.

How do i keep cut flowers fresh besides adding flower food in the vase?
Re-cut the stems under water after you bring home your cut flowers. Re-cut the stems daily. A small amount of chlorine bleach in the water will kill bacteria that accelerate wilting and decay.