Item Usefulness
Malarone 10 Nasty side-effects, but really no choice, and the other alternative, Larium, I hear is even worse.
Jeans 10 I had been expecting to wear shorts until my friend from South Africa suggested that wouldn't be a good idea.  I brought three pair of jeans, and wore a pair each day.
Plain Khaki-colored T-Shirts 6 I bought these because they were cheap, and because I had been told it was a bad idea to wear anything brightly colored because the animals wouldn't like it.  This turned out to be a little unnecessary (the other people on the safari wore whatever they wanted, and I could have too).  On the other hand, these lightweight shirts were inexpensive, appropriate to the climate, and they gave me something to donate at the end of the safari.
Ziploc Dry Bags 9 I'm glad I went to the large amount of extra effort it took to find these.  I purchased these heavy-duty Ziploc bags at Bass Pro, after searching in vain for something like them at several other stores.  They came in extremely handy, not only to keep related items together in my duffelbag, but also to keep things dry during those sudden "rainy season" showers.  Even though we were very lucky with the weather, there were a couple of times that items in my backpack (such as my camera and laptop) would have been at risk.  Making the extra effort to track these down was well worth it.  (And I hear they'll be even more useful at Victoria Falls)
Laptop 10 Some might say I was crazy for taking a laptop on this trip.  I wanted it to offload my digital pictures, and also to keep this web log.  I debated a good deal before deciding finally that if I DID take a laptop, I should not take the one I use for work (since it belongs to the company and not to me personally).  So my choice was either to buy one, or just buy a bunch of extra flash cards for my camera and keep the journal by hand.  I finally decided to make the purchase when I found one that was suitable both for travel and the other reasons I was planning to buy one at some point anyway.  While I guess I still haven't made it back home with it yet, I am happy to say it has survived the journey quite well (even the bumpy roads), and has greatly reduced the amount of time I otherwise would have had to spend trying to decide which photos to clear off my compact flash cards.  There's no way I would have known to buy 8+ flash cards (which is what I will probably have ended up needing by the end of this trip), and trying to decide which shots were worth saving with only the camera's tiny viewscreen would not have been a pleasant task.
Extra compact flash cards 8 At least one extra is just good common sense.  I bought a couple more as well.  While two would have sufficed just fine, having four gave me an extra measure of "backup" just in case my laptop got damaged or stolen.
Re-writable DVD's 8 Again, this was more for extra precaution to make sure my photos weren't lost if my computer disappeared.  I took over 7gb of pictures on the safari, and made backup copies to DVD before formatting the flash cards.
USB "jump drive" 8 This gave me the means to upload my web log.  Since I actually WAS able to upload it (for a while it appeared I wouldn't be able to), this purchase has been worth it.
Various items to make a "First-aid" kit 7 On my last sabbatical in Australia, I fell at Ayers Rock and had a nasty skinned knee that got infected, since I had nothing with me to properly treat it, and neither did the guides or anyone else on the tour.  I had a similar experience in Jamaica.  This time, I brought along rubbing alcohol, wash cloths, band-aids, and anti-bacterial ointment.  So far, I have only needed it the first day to treat a shaving cut, and the hiking on this trip has been minimal (it's hard to get injured just standing up in the vehicle to take a photo).  But given my history of sudden ankle-turns I was probably still wise to bring it along.
100% DEET spray 3 (9 for the 40% spray) This stuff is dangerous!  It leaked out into my bag and destroyed a plastic case I had next to it.  I have to think it can't be good for people either!  So, I got rid of it and switched to the can of 40% I brought with me.  We really didn't have much of a problem with mosquitoes and bugs anyway.
Wrap-around polorized sunglasses 8 I didn't use these at all until we got to Serengeti, but there they were a life-saver (or more to the point, an eye-saver).  The dust at Serengeti was bad enough that life with contact lenses would have been miserable indeed without these handy sunglasses to shield my eyes.  The polarization was a nice bonus as it gave me a rather vivid view of everything.
Bandana for dust 0 I didn't use this at all--the dust at Serengeti was bad, but not THAT bad.  The sunglasses to keep dust out of my eyes were plenty sufficient.