The photo says it all. I freeze two or three refilled Tropicana containers a few days before we leave. They are usually filled with water, but sometimes I make one with sun tea or gatorade. Remember to leave a few inches of air at the top for expansion.
Commercially bottled water bottles can be tossed into the freezer unopened, as can go-gurts. On day two of your get-away, you’ll have a nice supply of iced cold water from home. They do a nice job keeping picnic supplies cold, but you might want a big bag of ice to cool uncooked meat.