Here in the states, some dairies are providing quart size paper cartons for half and half and milk with screw caps to simplify pouring and sealing. The empty containers can be filled with water, frozen, and used to keep coolers and picnic baskets nice and cool. Just leave the cap off until the contents have frozen, seal and then keep them "on ice" 'til needed. Lots more cooling power than blue gel packs and most sealed envelopes sold for the purpose. Fill them with juice drinks instead of water, and they could do double duty - keeping surrounding things in a cooler chest cold, and they'll still be nice and "icy" hours after you set out on a trip!
