Friend, I’m about to reveal the secret to keeping lunch cold, and it doesn’t involve the expensive and semi-toxic (if you think about the mystery substance inside) ice packs sold in the store. Nope, the answer to your lunch woes is a super simple homemade ice pack made with just two ingredients already found in your kitchen. With five minutes of time, water, and a sponge, a ham-and-cheese-saving homemade ice pack can be made.