There are many things that can be done for colds & the flu. A multi-pronged approach tends to work best. For starters there are lifestyle considerations The following can greatly help your system.
1). Sleep-Get at least 8 hrs/night
2). Manage Stress-Through techniques of Relaxation, Visualization, Meditation, etc...
3). Nutrition-Eat nourishing foods such as fresh fruits and vegetables and eliminate sugar and processed foods
4). Exercise-moderate 3x/week
5). Be proactive-use prevention and take action if any symptoms appear.
There are many supplements, Herbal and Homeopathic Remedies that may be useful for colds and flu. Listed below are just a few of the common remedies.
Beta Carotene(avoid during pregnancy)
Many other remedies are useful but need to be individualized.