I don't know a lot about it, but they advise not to put it in the freezer. It is so cold already that it will simply cause your freezer not to run. And, I believe it will sublimate (turn into gas) at pretty much the same rate as if you just kept it in a cooler.
It isn't going to last for days in any case. Just put it in a cooler, try and fill air space with crumpled newspaper. If your cooler latches, do not latch it. Sublimation will build up pressure and it could be dangerous. Also be aware that while not poisonous, having a lot of dry ice in an enclosed space will eventually replace all the oxygen with carbon dioxide. Not likely, I know. Just be aware.
