Money
Both US Dollars and Pounds Sterling are the major currencies for exchange in Africa. Many tourist places accept US Dollars so you don't have to change as much to the local currency. The Rand is also quite strong in Southern Africa.
Travellers cheques are getting harder and harder to change every year.
ATM's are available in most major cities. It can be a bit haphazard wether or not they have cash stocked to give you or not.
I would strongly recommend taking US dollars, post 2000 edition in cash as well as having an ATM card with cirus or maestro as well as a pin number for your VISA or Mastercard.
In East Africa
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... most campsite bars, tourist activities and curio shops accept US dollars.
It is virtually impossible to change travellers cheques in East Africa, even when you find a bank that will change them it may take the bank an hour or so to do it.
Zimbabwe, current as at July 2007
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... tourists must pay for all accommodation by US cash or VISA card. (Zimbabwe only accepts VISA not Mastercard.)
All tourist activitity centres and shops accept US cash.