1 C 1/2 and 1/2
2 T sugar
1/2 t vanilla
1/4 C salt (we used rock salt, but I think other types may work)
First mix your 1/2 and 1/2, sugar, and vanilla in a small ziploc bag.
Fill a gallon size ziploc 1/2 full of ice and add salt and small ziploc bag.
Seal and shake for 5 minutes. This was the hardest part because the bag gets really cold and little girls get tired of shaking. So we wrapped the bags in towels and jumped up and down. They probably only shook them for a minute and a half, and I shook them for a little while. They still worked even with inconsistent shaking.