When my mother removes frozen vegetables from her chest freezer, she replaces them with clean, water-filled plastic milk bottles. The water freezes and helps to maintain the cold temperature of the freezer.
My family adapted this idea for camping trips. Instead of buying crushed ice, we reuse plastic milk bottles to freeze water, tea or lemonade for sipping while camping. The frozen blocks melt slowly over a weekend, providing cold drinks and keeping the cooler cold and puddle-free.