Gosh, that's quite a list! :)
1. What to pack on safari - have a look here tripadvisor.co.uk/Travel-g294206-c3322/Kenya…
Keep your stuff to minimum. Only today I gave an advice I usually give to my friends coming here: pile everything in one place 2 days before traveling, the next day reduce by half, on the last day make sure you have enough underware and reduce the balance of your stuff by half again. It will still be too much!
2. How cold - not cold that you have to have a jacket and gloves! Take a couple of long sleeve t-shirts/sweatshirts and a fleece, don't forget socks - you will appreciate them at night. You can dress up early in the morning in layers and then strip them off. It is really not cold (although it is a personal perception) and once the sun is up it will soon get warm. On safari most of camps/lodges put a hot water bottle into your bed. I suggest to take long sleeve PJ's for the safari bit as at night it can get a little chilli. But great for cuddling!
3. Black clothes - yes, lighter colour light trousers are better, khaki is the best as it does get dusty and you don't want to pack a pair a day. Swimming costume - no, don't buy another one unless you want to! There are no insects that will get attracted by the colour of your swimming costume.
4. Dress code. The best is to email your resort and ask them about their dress code. Everyone has their own. It goes without saying that swimming costume/bikini and bare torso for a man are a no no in a dining room, but I am sure this never even entered your mind :) Bring light clothes: shorts, light skirts, light dresses - this will be fine for you, shorts are fine for lunch. In many places it is customary to have a smarter look for dinner for men: long trousers and a shirt or a smart t-shirt with or without a collar. But there are places where shorts are fine for dinner too. So email your resort and ask them, if in doubt let your partner bring a couple of light trousers, he might also feel better in the evening looking smarter. In September evenings are nice and cool and wind can be strong at times, so for evening time bring something light - long sleeve shirt/top or a light cotton shawl/scarf which you can add if you feel cool or remove if you feel warm.
5. Culture / dress code. Thank you for thinking about it and respecting the culture. You can go around your resorts or in Diani area in shorts and a vest/t-shirt, it is a resort area so no problem there. If you want to visit the Old Town Mombasa & Fort Jesus, then have something a little more modest :) You can wear long or 3/4 trousers or a skirt and a t-shirt to cover your shoulders and not too open in the front, you do not need to have long sleeves though or cover your head. I see some girls dressed up in shorts and revealing tops in Old Town - of course they are not stoned :) but it is disrespectful as it is largely a Muslim area with quite deep traditions.
6. Spiders - this is Africa :) They might come through an open door or window but we really don't have huge scary ones in places where there is no space for them - resorts, hotels, shopping malls. They will be more scared than you to find themselves in a hotel room :) You can always step on it or ask a room attendant to deal with it. If it makes you feel better, buy a can of spray (Doom for example) in Nakumatt Diani and spray the offender!
7. Food and medicine - can't advise much, touch wood as we are from here we do not seem to have a problem :) Ask your GP or pharmacy. Also if you have this problem try to avoid eating leafy salads or even fresh salads at all, especially on safari, they can cause stomach upset if something is not washed too well. If this happened and nothing helps try this old method: 1 tea spoon of salt + 1 table spoon of sugar dissolved in a glass of water - drink as much as you can. This is a rehidrant and it also helps to stop runny stomach. Flat Fanta Orange diluted half-half with water will also help to rehydrate. Activated Charcoal is good, I am not sure if you can get it where you are. Also drink only bottled water and brush your teeth with it as well, again especially on safari - this is a precaution. Bring some sachets of rehidrant anyway just in case.
8. Other advices: check that park fees are included in your package, take a lot of memory for your camera, don't forget sun cream, in the evening apply mosquito repellent to open skin, especially ankles, don't think that of it is cloudy you will not burn as you will :) - so apply suncream even if it's a cloudy day, drink plenty of water especially on the coast. And last but not least - enjoy your trip!
If I think of anything else I will let you know.
Edited: 3:55 pm, January 17, 2013