Can I bring my San Diego Zoo souvenir cups that I bought the day before, and use it to get my drinks?

There is a minimal charge to get a refill with cups that had unlimited refills on the day of purchase. They are not restrictive of the cups, containers, and food you bring in.

Sounds like a great idea, I don't see why not

Yes you can and it saves you a little bit of money.

I don't see why not