Feeding pumped milk on the go

I'm a FTM and EBF right now but have been pumping and freezing for when I go back to work so grandma can warm and feed while I'm away. I'm using the Kiinde storage system so I pump directly into the same bags I can store, warm, and feed from, no transfers. In October we have a family wine tasting trip planned so I'll obviously have to feed him stored milk for the hours we're out, my question is how do I travel with my defrosted breastmilk? Do I need to bring a warmer with me or can he eat it cold or room temp? I know I'll have to bring my pump to pump and dump while I'm drinking so my supply doesn't go down but how am I supposed to feed my little man that stored milk on the go?