You can also take empty 2 liter bottles and fill them with water and freeze them along with the food. They will add extra cold "thermal mass" that will help keep the freezer cold longer. When they finally do melt, they also won't make a mess since they're contained in the plastic.
Advantages the "blue ice" freezer packs all have as well, except if you buy soda pop, the bottles and water are free.
One thing you can do with the pop bottles that you can't with the "blue ice": If you clean the 2 liter bottles carefully with a little hot water and bleach, and then add a drop of bleach to the fresh water you add for long term storage, you can use them as an extra stash of emergency drinking water. If power is out long enough for them to melt, you may well need the water.
We allways make ice this way for the "food cooler" as opposed to the "drinks cooler" when we go camping, that way, as the ice melts, it dosen't make the food soggy...