Bag friend

The friend in the group that always carries a bag with them, usually a tote or a large purse. Helpful for when you don't want to hold your wallet or phone. They usually have mints and shit in there too.

Amy: I want to bring a water bottle but I don't wanna hold it the entire time we're out
Katie: Jessica always brings that big ass bag, she'll probably hold it for you.
Amy: Gotta love having a bag friend