Some foods are very high in potassium.
V8 12oz has 680mg
V8 low sodium has 800mg (this is approx what an RX supplement has in it).
1/2 cantaloupe has 1200-1500 depending on its size.

OTC supplements have a maximum of 99mg/tablet and I think are not cost effective for potassium supplementation.

A serving of Gatorade is low... 30mg

The new nutritional RDA for potassium is 4500mg/day.
This has been raised from 3.5 gram previously.

This website can help you choose high potassium foods:
http://www.nutritiondata.com/

Many people do not get the RDA in potassium. If you look to your diet, you can fix most low potassium levels safely with wise food choices.
Taking supplements when you do not know your serum level, or kidney functions can be dangerous. Some kidney disorders leach potassium and some conserve it.

Some drugs leach potassium: many diuretics, steroids, diarrhea,
some antibiotics.
Some drugs conserve potassium: spironolactone, triamterene, amiloride, ACE inhibitors for blood pressure.

So please do be careful.