Hi Angie!
I actually live about 30 miles south of Rosarito, in Ensenada. I have not actually partied in Rosarito, but I can answer some of your questions.
You should not have any problems coming back across the border with your dog...but, I would bring any paper work you have on him/her with you (copies of the latest shots, etc.).
PAPA'S N BEER! We have one here and it is soooo much fun! And the one in Rosarito is twice as big and is right on the beach. I know that there are a couple of good other places to go out, but I don't know their names.
It is a little dangerous there. One of the reasons I have not gone up is because it would just be my sister & I and that worries me. But, since you will be in a large American group you should be fine. Just keep your "feelers" up!!
And try to stay together as a group.
We bring food down from San Diego all of the time, so that is not a problem. I just wouldn't bring any Fruit because they are very particular about Fruit being brought down. They used to have a check point on the freeway.
Anyways...I hope you have a fabulous time!!!! Party Hard!!!