I believe you guys are looking at this at the surface level, when there is much more to it.
"Always have a backup chick" could mean you have a plate or two on speed dial, a side piece to your main course, or maybe just the illusion of another woman. LEt me start with listing a couple examples for the third possibility, because the first two are just plain obvious. Having a woman that you can dial that is down to fvck is not a high quality woman, no other way to put it. And the second is just a man that values infidelity. Those two are very cut and dry. But the "illusion" of another woman is the type of covert communication a woman understands very well. This happens often in relationships. Here are some examples..
-a man has a female co-worker, the co-worker is attractive, and responds well to the man's natural charm. The man invites his lady to a company gathering where she witnesses his affect on his female co-workers. She will think, "he could have a backup chick"
-a man travels somewhere with his lady, takes her on a great getaway to Hawaii. During the trip, the man naturally converses with others, and women react to it. Even though they are on a trip together, she will think, "he could have a backup chick!"
-a man has female friends that he sees rarely, but gets in a large gathering. His lady witnesses how this man charms the women, women he has only seen rarely on special occasions, and thinks "he could have a backup chick"
A high value man will naturally make your woman jealous without even trying, he will make women gravitate towards him without even trying. His actions will be completely innocent, but she will be able to observe how other women view him. She will realize he could be fvcking any one of them. Depending on her level of security will determine her actions. A secure woman will feel proud to have such a man, while an insecure woman will not. She will throw him a ridiculous amount of flack for doing absolutely nothing.