Though it's easy to keep ice hard indefinitely when you have access to an electric freezer, there are times when this option isn't available. Parties and other hosted events, especially warm-weather, outdoor events, often require that the ice come out early and stay out for a long time. Though eventual melting is inevitable in these circumstances, there are a number of ways to keep the ice colder longer.
Put ice in reflective containers. If the outside of the storage container reflects sunlight away rather absorbing it, the container and its contents will stay cooler. If you don't have a reflective container, simply wrap the one you have in aluminum foil.
Keep cold and icy things close together. As ice warms, it gives off a flow of cool air to the surrounding area. This warming is slowed, however, if cool objects are stored close together and can keep the surrounding area cooler. Even placing ice next to items that are merely cooler than the room or outdoor temperature, such as a fruit platter or punch bowl, can slow the melting time.
Use insulators. They are materials that inhibit the flow of heat in either direction, making them just as effective at keeping things cold as keeping them cool. While coolers and ice buckets are usually designed to be insulating, you can amplify this affect by wrapping them in thick blankets.
Store ice in shady areas if outside. If you have a shade tree, umbrella, or can keep the ice under the serving table, it will stay cooler longer (keeping ice lower to the ground will also help, as heat rises and the ground stays cooler).
Use ice in the largest pieces possible. Smaller pieces of ice have more surface area relative to their mass, which means more exposure to warm air. This means that the larger the pieces of ice you have, the longer they'll last, even if the overall quantity of the ice is the same.
Favor lighter colors in the sun. Darker colored containers, tablecloths or other objects in the vicinity of the ice will absorb heat and make the surrounding area warmer, while light colors and whites will stay cooler.