For many, many years the longstanding source of potassium has been bananas. I can remember various coaches telling us to eat a banana or two during the first weeks of the season to prevent soreness and leg cramps.

The average banana, the edible part, contains anywhere from 400 to 500 mg of potassium in it. About 39 mg of potassium is equivalent to 1 mEq. The average a banana has about 10.3 to 12.8 mEqs of potassium.

Roughly one banana is equal to a 10mEq tablet of Effer-k, or half of a 20mEq tablet.  The distinct advantage of Effer-K is no banana taste; which many do not care for, including myself.

http://forum.onlineconversion.com/showthread.php?t=11451
http://www.buzzle.com/articles/how-much-potassium-in-a-banana.html
http://www.diagnose-me.com/treat/T154575.html