I know it sounds gross but as much raw garlic as you can handle. When I get a cold I peel about 5 medium cloves and cut them into pill sized pieces and just take them with tons of water. Also cayenne pepper in water is good too. The most helpful thing I've found though that doesn't taste disgusting is elderberry extract. You can find it at health food stores, be careful though it can be alcoholic and non-alcoholic so just be sure to double check so you don't get liquored up. Just a few drops in water several times a day boosts your immune system big time.
Honey and lemon juice made into a hot tea... Works great aslo drink chamomile Tea......