"Whip-it's" are Nitrous-Oxide aka Laughing Gas aka NOs used by your dentist when performing oral surgery and to make your car go really fast. It is supposed to be used in this case to fill Whip Cream canisters.
Once again I find myself ill informed. I can't ever remember having or even considered buying a Whip Cream canister that needed to be filled. The canisters I'm familiar with came from the store already filled with Whip Cream.