For fungus on your feet, especially between the toes, apply a baking-soda paste, Take 1 tablespoon of baking soda and add a little lukewarm water. Rub that on the site of your fungus, then rinse and dry thoroughly. Finish off the treatment by dusting on cornstarch or powder.
-Prevention Magazine, The Doctors Book of Home Remedies

Soak your foot in a mixture of 2 teaspoons salt per pint of warm water, says Toronto podiatrist Glenn Copeland, D.P.M. Do this for 5 to 10 minutes at a time, and repeat until the problem clears up. The saline solution helps provide an unappealing atmosphere for the fungus and lessens excess perspiration. What’s more, it softens the affected skin, so antifungal medications can penetrate deeper and act more effectively.
-Prevention Magazine, The Doctors Book of Home Remedies