I used some of that reflective bubble wrap stuff everyone uses for cozies to make a thick pouch thing. I took a 3 oz piece of dry ice, wrapped it in paper and then put it in a sandwich baggie (not totally sealed). It has kept 6 popsicles basically frozen for 32 hrs so far. The dry ice is almost gone now
I think it would be best with things that just need to be refrigerated.
Another idea would be some sort of container with a absorptive fabric shell. You could get it wet and the evaporating water would cool what's inside.

