THE MOST IMPORTANT THING no questions asked is BOOTS!!!!
Unless you are the kind of person that needs a 1907 period correct costume (and by the looks of some of the catalogs, these people must exist in large number!) $100 can buy you perfectly acceptable clothing in Africa in a worst case scenario. No amount of money on earth will get you a properly fitting broken-in set of boots. Even bespoke hunting boots need to be broken in.
I usually travel with two pairs of hunting boots: one in the carry-on, one in checked luggage. Last year, I needed to replace one of my two pairs of hunting boots. I saw a pair of boots I wanted when I was in Namibia in 2011, so when I went back in 2013, I traveled with a pair of boots in the carry-on and intended to buy the boots I wanted in Windhoek upon arrival. Turns out the company moved or went out of business or something and we couldn't get the new pair of boots. No problem, I had my regular boots in carry-on. When I put them on the first day, I discovered to my horror that somehow, despite being in carry-on, they had been damaged some how such that there was a fold of hard leather impacting painfully into the top of my toes. No effort fixed them. I ended up hunting several days in sandals until discovering that my PH happened to have a new pair of exactly the boots I was hoping to buy, and in the size I wear!! Break-in was still uncomfortable but fortunately, the situation was that my wife was leopard hunting and my son was out for honey badger, and I was there for moral support and to sit the occasional water hole. Bullet dodged.
The new plan is one pair of hunting boots ON MY FEET for the travel and the other pair in the carry-on either with shoe trees in them or stuffed full with socks, etc.
As far as clothing goes, I really like to travel light. Africa suits this as there is generally laundry service, so one change of clothing is all I need. I really like tropical weight BDU pants (I prefer to remove the thigh pocket). They are loose and the adjustable waist band means it is easy to fit long johns under for the morning chill. I actually use heavy fleece pajamas as long johns and then I've also got them as pajamas if it is cold at night. Double duty and versatile.
I've worn T-shirts, but I prefer a brown golf shirt. The golf shirt is more presentable for a trip into town. If I could find a pair of lightweight chinos with a fairly loose fit at the knees, I'd go with those because they would work well in town and the bush. I find pants that aren't loose at the knees really add to the effort of walking. If you remove the thigh pockets from the BDUs, they look halfway presentable in town. For a dedicated hunting trip, packing is easy. If you add in trips to town, or you are staying in Europe for a week before heading to Africa, or whatever, you need more and that adds weight and volume.
A hat is important to me to keep the sun out of my eyes; I use an old boonie hat when it is hot. I picked up a German wool hunting hat that I like and is kind of warm enough for cool mornings, but really a wool watch cap would travel better and be warmer. However, I dress for the plane- jacket, tie, etc so I can wear my German hat and it looks reasonable and it doesn't add to my load. I like to dress for flights, just the way I was raised. I think one gets treated better throughout the airport/airline experience if one is dressed well. I had a travel jacket specifically made with extra pockets for tickets, passport, American and destination currency, etc. I look presentable, I can go to a decent restaurant, I have all my stuff readily at hand, and it works as a blanket on the plane if I need one. If I put a sweater underneath, I don't need a coat in most environments (if I'm wearing a jacket, I'm probably in an urban area and will only be outside for a short period of time). A no-iron shirt completes the plane/ nice places ensemble and I don't have to pack it. I wear it on the plane and take off what I need if it gets warm. The sweater works double duty on the hunt- I get cold easily; I grant I may bring more clothing of this sort than the average person. A knit sweater is not a good outer layer in the bush: it picks up seeds and thorns and everything else. The sweater is a layer worn underneath something else. I happen to like a heavy wool button-up shirt in the bush if it is cold; others may differ. Mine is a Korean war surplus job that I got for $3.
In the carry-on is always a change of socks and underwear. I've had my luggage lost for as long as 4 days and was able to do fine by washing socks and underwear in the sink. You can wash the no-iron shirt and it comes out OK, but if you are wearing it every day prepare to start the day off wet if you are just drying it on a hanger in the hotel room.
Travel light and plan double duty for everything and you won't be sorry.