I get foot cramps too… mine are right in the arch and form a huge knot that is visible. The only way I’ve found to get rid of them is to press as hard as possible on the knot while screaming bloody murder.
Maybe tonic is a better idea.
Flat-footedness and weight/exercise have been mentioned. In the interest of adding more data points, I have normal feet arches and experienced cramps most at the peak of my fitness last year (when I was under 10 per cent bodyfat).
Maybe increasing consumption of G&Ts is the answer. 
In order to expand on my previous post, and provide some more data points for our highly unscientific research:
- Not flat footed
- No weight problem (BMI of 21)
- I don’t take any type of medication.
- No special diet. Just normal food.
I guess it could be a lack of (or perhaps too much of) some type of mineral although I have no idea which one.
Hmm. Screaming bloody murder. I’ll have to give that a try while I wait for word on my G&T related research grant.
Podkayne: I did all of those things too - healthier diet, taking up yoga etc, and I do indeed suffer cramps much less often than I used to. And thanks for the pose - I’ll try it later on, it looks like my feet would like it too !