Have you ever worked as a professional magician?
There are two main reasons why I carry more than one deck of cards with me to a restaurant gig. First of, I get people to sign the card more often than not, so after only 10 tables, my deck is pretty slim, so I have to have a spare one in order to work properly. Second reason is that usually, only one of those decks is normal, the other one would be gimmicked/gaffed. So if you do invisible deck at one table, and the table right next to that one invites you to perform, you cannot do the same trick, specially if it's not reset yet.
You don't need any fancy deck switches or slights, you just put a deck in your pocket, and when you get to the next table, take the other deck out.
And btw. if you have a hard time remembering in which pocket you put which deck, then you need to be wearing a helmet.
Also, you are a working professional magician, NO ONE WILL EVER question why you have more than one deck on you. It's because you're a professional magician. If someone ask you (during a professional gig), why do you have more than one deck, then they need to be wearing a helmet.