Anyone planning an African expedition in the classic era will enjoy the Handbook to British East Africa and Uganda. Although it dates to 1912 it's filled with the kind of color that really brings something like Masks of Nyarlathotep alive. That includes a helpful list of supplies for a three year expedition, recommendations for clothing, the intricacies of tribal relations, and two traveler's dictionaries for the local languages.
You'll also find a heaping dose of the casual racism of the colonial period, including multiple instances of the natives being referred to as "niggers", so be forewarned. What makes it even more surreal is that the author seems to have a genuine appreciation for the people and cultures of the region. One section includes a telling comparison of the supplies needed by Europeans with the minimal requirements of the locals.