If you don't know how, get a manual or ask a neighbor with a similar garage door. You don't want to have to go to a detached garage in the rain when you need it. Allow at least 2 gallons per person per day. If the tub has a built-in lever stopper that leaks you will have to buy a rubber one and use it to work around the leak. A full freezer retains cold longer.
Spoilage starts after one week in unopened freezers even in the absense of electricity.
Also, turn the temperature selection to the coldest setting. One Coleman-type cooler is devoted to food, with just some ice. The other cooler is just bags of ice. Take pictures and video. There is no need to develop the film unless needed.