We are now in The Gambia and we still WANT mail; letters, packages, postcards, anything. 

It will be best (cheapest) to send light things through the US Post office.  If you are sending a package there is a handy flat rate box that works internationally.  Valuable things may get stolen and our mail may be opened. Number your letters, pages, packages, and include an inventory because sometimes letters, pages, packages, and the stuff inside ends up missing.  Air Mail will work the best, as surface mail means it will be on a boat and then a truck.