The most obvious way charities benefit is from the auction of the cars at the destination (yet to be decided).  Experience from the Plymouth Banjul Challenge is that the cars sell for quite high prices, typically around £750 for a medium size saloon car and £1,500 for a 4x4.  They'll also auction any old camping equipment you don't want to take back to the UK.  All the proceeds are distributed to local charities with the accounts made public.

There is no requirement to raise sponsorship.  However many people and organisations are only too happy to help with supplies, discounts on equipment or cash.  You can offer to put a sticker on your vehicle and local papers, radio and TV stations can be persuaded to provide you and your sponsors with free publicity.  International and UK charities can also benefit by raising money through websites like http://www.justgiving.com/. 

You can also help the people of the countries you pass through by taking with you medical and educational supplies.  You can arrange in advance to take them to a specific school or clinic or just find one on the way.  The most basic medical supplies like bandages, plasters, aspirin etc are all in great demand as are pens and school exercise books.  Its best not to take prescription medicines unless you make special arrangements. 

You can also help people directly on the way by giving away "cadeaux".  In busy towns and at borders you are likely to be approached by children and adults asking for "cadeaux".  Some people refuse as it encourages what is effectively begging but pens, footballs, toothbrushes and old T shirts are very gratefully received.