Obviously a decent field guide is a must. The consensus seems to be that the best guide to the region is Birds of Southern Africa authored by Ian Sinclair et al.
This guide was most recently updated in 2011 with the publication of the 4th edition. It is interesting to note that the project is funded by Sasol, a South African industrial chemical manufacturer, presumably as a public relations effort. The South African version of the guide (pictured above right) is not available in North America, however the Princeton Field Guides version (pictured above left) is readily available. This is yet another example of Princeton acquiring the rights to produce and distribute a regionally produced field guide to the North American market.
In addition, there is an electronic version of this guide produced by mydigitalearth that is compatible with Apple, Android and a variety of other platforms. The icon for the app is pictured above. The great thing about this version is that it is supported by sound recordings for most of the species included in the guide.
Next is a birdfinding guide to the region. Southern African Birdfinder is the most detailed and up-to-date publication of this type available. Like the field guide, this book was also funded by Sasol.
Although it is not related to birding, what would a trip to Africa be without seeing some of the mammal life? Surprisingly I was unable to find much variety in the way of mammal field guides, however The Pocket Guide to African Mammals by Jonathan Kingdon is widely recommended, reasonably comprehensive, affordable and compact enough to make it the best choice I could find. There is an app available for this book as well, but I didn't bother with it.
A handy thing that I will be using on this trip for the first time is BirdLog - Worldwide which you might have seen profiled recently in this article from eBird. Entering our bird lists every day or so will be less of a chore than having to enter them all upon our return home, and the sightings should be more fresh in our memory as well which should aid in more detailed notes.
In addition to the above, we have a detailed road map (although we will likely supplement it with a road atlas upon our arrival) and an African news app. Of course this isn't everything we consulted in our trip preparation, but these are the resources that would likely be of most interest to birders.