Used usually in a way joke by a friend of one to another who is currently in a relationship. In a way, "Don't forget the Drop n' Chop" is like saying "Don't forget to get sum"
A chopping motion of the hand can be used for emphasis
John: "Hey so how'd it go with that chick
you saw at the mall?"
Jeff: "It's all good. I gotta date man!"
John: "Ey....Don't forget the Drop n' Chop!!"