Remember that ol’ maxim, “feed a cold, starve a fever”? Forget about it. Eat food in both cases. You don’t have to eat much more, but you should eat healthy. More imporantly, you need to stay hydrated as well.
How about the age-old remedies of chicken noodle soup and lemon teas? There’s nothing special about either outside of the fact that they’re hot and can help soften mucus. The same can be said about most over-the-counter supplements.
So, in the end, just make sure you’re drinking lots of water and eating a normal amount of healthy food when you’re sick. Your body will do the rest. There are no tricks.