Is it me or is this odd behaviour?
I have a friend who brings her own drinks to my house, e.g. a can of coke in her bag.
My in-laws do it too and I can't get my head around it. It's not like bringing a gift, they bring stuff for themselves. They bring stuff they like, rather than stuff we like, so it's not a gift. Though they do attempt to offer things around sometimes.
Am I missing something? I wonder if they don't want me to buy stuff for them, but I do obviously and then just end up with twice as much because they've brought their own!