Put 1 gallon of water and salt into an 8-quart pot. Bring to a boil over high heat. Put the remaining 1/2 gallon of water and the ice into a container. Set aside. Add the squash to the boiling water and cook it for 3 minutes. Immediately drain in a colander and then transfer to the ice bath. Shock for 3 minutes, replenishing the ice if necessary. Drain the squash and transfer it to 2 half sheet pans lined with 3 layers of paper towels. Pat dry with additional paper towels. Remove the paper towels and place the pans in the bottom of the freezer until frozen, about 1 1/2 hours.
Once frozen, transfer the squash to a 1 gallon resealable plastic bag. Lay the bag flat on a counter and using a straw, suck out any remaining air in the bag. Label and return the bag to the freezer. Serve the squash frozen.