Finding yourself outdoors without an ice chest requires some ingenuity to keep ice cold. Take stock of the items you have available, and put them to good use. Insulation, reflection and the right location are all key factors in keeping ice cold for as long as possible.
Place bagged, cubed ice inside a container such as an insulated or styrofoam cup. If you don't have anything like this, a bucket, bowl or any waterproof container will work. For block ice, chip off the largest sized chunks that will fit within your container(s). To keep food cold, place it on top of the ice.
Place a can koozie, such as those for soda or beer cans, on the exterior of any container that it will fit around. Be creative--- if the koozie will fit over the top of a graduated container and not the bottom, place it over the neck. The idea is to insulate as much of the container as possible.
Find a cool spot out of the sun to place your container(s). If you are camped close to a stream or lake, the water is usually the coolest place. Secure your container(s) between rocks, or tie to an anchor on shore.
Set your reflective material over the top of your container(s). This will deflect the sun's rays if your cool spot gets any light over time. If you placed your container in a stream, mould the foil over the top; if you are using a sun shield or tarp, tie it in place or secure with a rock.
To keep your ice cold after fashioning your makeshift cooler, handle it as little as possible. Keep it covered until you need it. For food storage without a cooler use several smaller containers rather than one big one. The less space there is for air to circulate around the food, the less cooling properties your makeshift ice chest will have. Periodically drain the water from your containers. Water will make the ice thaw more quickly. Larger chunks of ice stay colder longer so don't break up those cubes that have fused together.
Don't take chances with perishable proteins. Meat and poultry need to be cooked as soon as possible if you do not have a way to keep it at a temperature below 4.44 degrees C. Store the cooked protein in your makeshift cooler; this is safer than attempting to store raw meats. Keep a separate container for ice you will use in drinks. Don't store food in the same container you will use for beverage ice.