Place the heavy cold items, such as milk and packages of meat, in sealed plastic bags to prevent cross-contamination. Then place them on the bottom of the cooler.
Wrap and insert frozen vegetables and flexible ice packs in between as many of these items as possible. Put them in the middle between items, rather than along the edge of the cooler, so that they touch at least two items.
Layer smaller items, such as packages of cheese and yogurts, on top of the heavier items and then place a layer of frozen vegetables or ice packs on top. You do not have to cover every square inch of the layer, but the more ice packs, frozen vegetables and other frozen items you use, the longer the cooler will stay cold.
Add a third layer of food and drink if there is room and top off with another layer of ice packs or frozen vegetables, if possible.
