Hi Sandy
It's difficult to say how much you should take because some people spend quite a bit and some don't spend very much at all. But I would say you should take at least £20 a day to make sure you have enough for food, drink and a few souvenirs. That said, you could probably get by on around £10 if you are very careful.
For Zambia, you could change some Sterling on arrival, and possibly any leftover rand you might have.
Personally, I wouldn't bother with travellers' cheques as they can be a hassle to change.
Kind regards,
Olly, your editor