I have had similar problems. Best luck I have had is to put them in a zip lock baggie. If the cold packs break, one more barrier to go through.

Take a look at these cold packs. Best ones I have used so far. No smacking or popping of inner bag to activate. All you have to do is pull on the ends and the plastic clip in the middle pulls away and allows to the 2 chemicals to mix.

http://online.boundtree.com/store/product_index.asp?Cat=&SubCat=&Prod=952000