Last time I went to Africa (Tanzania), I had a 35 pound weight limit. That was for the internal flights on tiny airplanes. For example, there were just the two of use with our driver waiting on a dirt airstrip in the middle of a savanna and a tiny plane flew in, the pilot came out - he said "Hi, I'm X, your pilot." There were no seat assignments because we were the only two passengers.
I used a duffel with wheels, but no extension handle - that cut out at least 5 pounds off other luggage. I brought bubble wrap and duct tape for souvies, old clothes to wear on safari and then leave at the hotel/lodge/camp (housekeeping could keep or recycle), some twine to use as a laundry line, liquid laundry detergent in a mini-shampoo bottle, a nice DSLR camera, a small back-up camera, meds and additional antibiotics for what-if situations, moneybelt for cash and credit cards, couple of books, nice binocs, extra contact lenses, back-up glasses, sun glasses, zip-off pants (two pairs of pants in one), flashlights, mini-LED lantern, diary and pens (to write my trip report), fleece jacket, snacks, and more. You can really get a lot in a small duffel if you put your mind to it.
I haven't been on the S. Africa ABD (I just made my reservation), but on the Galapagos trip it was completely casual, even at dinner. And on my previous safari, it was casual at dinner as well - and I stayed at some really fancy hotels, lodges, camps - at one lodge we had an honest to goodness butler!
