Another possibility is potassium. When I get cramps (mine are usually around the ribs), that's the primary culprit. A banana or two typically takes care of it. In a pinch, a small amount (think a fraction of a teaspoon) of potassium bitartrate a.k.a. cream of tartar works too. I find the taste weird but tolerable, but I'd still recommend having water ready as a chaser.

Just don't go too crazy wild with potassium, as an excess can cause heart problems.