Final answer:
A cold sandwich should be kept refrigerated until it is served to prevent the growth of harmful bacteria. Perishable leftovers should be discarded if left at room temperature for more than two hours.
Step-by-step explanation:
According to food safety guidelines, a cold sandwich should be kept refrigerated until it is served to prevent the growth of harmful bacteria. Perishable foods that are left at a temperature between 4 and 60 degrees Celsius (40 and 140 degrees Fahrenheit) for more than two hours should be discarded. This is because bacteria can multiply rapidly at these temperatures, increasing the risk of foodborne illness.