Cooler Shock ice packs absorb heat from both sides. Understanding that, consider allowing both sides to work for you for best performance. If you place the pack directly on the bottom or in direct flush contact with the sides of a cooler, you are using the ice pack to absorb heat through the cooler wall and then from the outside. Said another way, you are cooling the wall of the cooler and the outside. For many on a one day trip this is probably irrelevant. For those that want the most out of the pack, place it so that it is not in direct contact with the floor or sides of the cooler. You can do this by placing beverages under it or use basic bubble wrap to create an airspace.
For those taking multiple packs for multi-day use, stack the packs (still using something to keep the bottom pack off the floor of the cooler (bubble wrap again). As the upper packs give off their energy, remove them and expose the next pack. By doing this you are using the upper packs as insulators for the lower packs thereby not allowing them to all cool at once.
Conversely, when freezing your packs, create air space in between them when placing them in the freezer to get the highest energy absorption in the shortest amount of time. One way is to spread them out on different shelves.
Yes, there is a science to this and you will have a much better experience when armed with knowledge.