Going on a trip without baby - EBF help

I'm going to be away from my baby for about 12 hours next week. I've got milk saved up but I have two important questions. First how do I make sure it doesn't effect my supply? I only have a manual pump and milk catchers. Should I express when I can? It's a concert so I won't have but maybe one or two chances to do that the whole time I'm gone. And second, how do you thaw frozen milk? Do you run it under hot water until unfrozen? I've never had to do it.