I'd have to vote for the sharp knife thing...The blade on a Charge or Wave seems to do nicely.

Depending on what it is, and how it's packaged, sometimes you can cut just enough, far away enough to pry the rest open with your fingers.

Barring that, I try to use just barely more than the tip, so the blade stays away from the goods. Of course, a sharp knife helps that whole process work.

Another thing you might try is moving the blister pack instead of the knife...a trick I learned the summer I failed at selling Cutco. I wasn't cutting blister packs of course, but when using the Chef Knife, we were encouraged to move the food we were dicing toward the knife instead of moving the knife toward the food...same thing works for blister packs...if you keep the knife in one place, then if there is a slip, it's the pack...you might smack yourself in the chest, but there are no lacerations