Before our last trip we invested in a small plug in cooler that worked very well. We paid $30 for it at Walgreens. It is only large enough to hold a six pack, but we kept a couple of half pints of milk in it, our son's medication along with packaged lunch meat and some yogurt. All of the less perishable stuff we kept in our other cooler which keeps things frozen for up to five days (it would probably be ok for milk, but I am a bit squeemish about my dairy products.) I am considering buying a larger plug in cooler so we can keep half gallons of milk and OJ and more yogurt in it. This would save us from buying the half pints in the hotel for $1.75 each (and to think I pay $1.92 a gallon at Sam's Club...)
It would, however take awhile to recoup the cost of the new plug in cooler ($65-$80 depending on size). Hmmmmmm......