This unknown is probably the greatest magnet that is Africa.
Planning for a trip/expedition across Africa should thus never be taken lightly. If you can think of something that can go wrong, add it to your list of back-up solutions required for the trip. Of course, in an ideal world, everything will go as planned and nothing will go wrong or awry - just remember, ideal world is pie-in-the-sky when we're talking Africa.
Let's start with the basics like documents you should always have with you. Personal details and contact details of family and/or close friends summarised on one sheet goes a long way to putting in place a good chain of communications should something happen or go wrong. This contact sheet should be sent to each of the family members/friends you want to keep in the loop. That way if one gets a call for assistance, they can contact one of the people on your contact sheet.
On arrival in your destination country, it's also prudent to let your contacts know what your local mobile number will be. (Local sim cards mean cheaper calls abroad as opposed to very expensive roaming fees)