Discover the perfect Insulated Lunch Bag addition with our picnic backback.To choose the right size insulated lunch bag for school, measure the lunch box or containers you pack most often and pick a bag slightly larger so there’s space for an ice pack and snacks. For younger kids, a bag about 8–10 inches long usually fits a sandwich, drink, and snack. Older children often need a 10–12 inch bag to hold larger containers, drinks, and an ice pack while still fitting easily in a backpack.