Two interviews in the same day, what to do if hired by both?

So I applied to a bunch of food service/retail type jobs a little while back and some of them are just starting to respond to my applications. I have two interviews on the same day this week, and I was wondering what I should do if I were to be hired by both? If they hired me on the spot, but I still have more interviews, what should I say? (Of course this is all IF I get hired!)

Also, I applied to many other jobs, so what do I do if I just started a job but one that I want more contacts me soon after?

Any advice would be appreciated, thanks! :)

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