Stranger things have happened.

While I think it's a bit of a long shot asking an airline to pick up the fare for you college summer vacation (even it is for a decent cause), it never hurts to ask. If I were you, I'd do the following:

1. Find out which airlines fly direct to South Africa from the US. United and Delta come to mind.

2. Put together a professional proposal/presentation discussing what you are trying to accomplish. Be creative! I'd consider a video presentation, a powerpoint presentation, or a very well put together paper-binder presentation.

3. Emphasize how your efforts will bring glowing press to the airline, at minimal cost to them, while helping actual human beings. Will you document your endeavors? Send regular pictures and updates? The fact is, your work will at best be a blurb for the airline in the US. HOWEVER, airlines love good press in the countries they serve, and this is where you'd like to focus your efforts.

Do some research on the airlines that are possibilities, then send your presentation to their PR department. Most large airlines also have HR departments that eat this volunteer stuff up.

Also: I wouldn't ask for a "free ticket", per see. Your presentation should indicate your willingness to fly "space available". That is, the handout you're looking for from the airline should be: If there is an empty, available seat on the airplane, would it be possible for you to have it just for the cost of mandatory taxes (both the US and the host country are going to levy a marginal fee, say $200?). This costs the airline nothing, and in return the airline gets good PR for free.

Good luck. FWIW, I think the "organic food for the poor" is a little silly; no bona fide starving person is going to give a rats behind if the food they're eating has a little "organic" sticker on it. You might consider that others may have this jaded impression when reading your presentation as well, so tailor your presentation accordingly.