20 amps? 30 amps?
Must be a contest in the south. In the northeast, if we use more than a few hundred watts we pop the breakers. We get 2-4 teams sharing a 15 amp circuit (1650 watts @ 110v) at most events. (Hudson Valley, Cape Cod, and Troy being the exceptions - thank you organizers!)
Your guru and your ipod are going to use under 2 amps. 20 amps is more than enough for what you are doing.
By comparison, home circuits are generally 15 amps. A refrigerator, microwave, or small air conditioner will draw 10-13 amps, which is why those kinds of appliances are best used on a circuit by themselves. It's also why most comps in the northeast tell you that you can't use a refrigerator.
30 amps is generally for motorhomes, which tend to require either 30 or 50 amp feeds if they are using an electric refrigerator or AC.
Gerrit_Boys is also right about the cords. The longer the extension cord, the more power you lose over the length of the run. If you have a 100 foot cord, get at least a twelve gauge cord. (The smaller the number, the LARGER the cord is. Smaller numbers are better for long runs. If you are using over 12 amps, get a 10 gauge cord. An fridge or AC unit running on a 12 gauge 100 foot cord will cause the cord to overheat.)