Nairobi to Kigali route:
Money - can pay for Kenya visa £30 or $50; can exchange sterling or dollars just before airport exit; can exchange either at Jinja - better dollar rate if $50 notes or larger, but better rate for sterling anyway; but you do need dollars to exchange in Muzanzi (Rwanda); for Uganda visa ($50); for tips to local guides (smaller dollar notes); for Masai village visit ($20); if you want a tour T shirt ($20); and cheaper to pay in dollars for boat cruise to the source of the Nile at Jinja ($15) although you could pay with local currency. Guide's recommendation for how much we needed in Kenya was over generous - $100 each was far more than we needed - (but you can exchange it in Uganda or use it for the crew's tips) but his recommendations for Uganda ($50) and Rwanda ($50) were not enough, you definitely need to change more. Exodus estimate of tipping was about 1/3 of what we were actually advised to tip local staff (excluding Exodus crew - and there were 4 of them so you need to budget for that too).
Food - absolutely fine and you can buy snacks at supermarkets along the way; recommend taking something to spice up your food and provide protein if you are a veggie - I took marmite and peanuts (or you can buy peanuts at supermarkets there). The crew normally brew up after dinner but if you want decaff drinks ibring some herbal T bags/decaff coffee.
Clothes - in Dec/Jan it got chilly very quickly from late afternoon in Kenya, and at Lakes Bunyoni and Mburo in Uganda - and was really cold overnight sometimes. Recommend thermal layers (or for women, 60 denier tights work well), woolly hat, fleece and scarf/gloves if you feel the cold. It was also pretty chilly in the daytime at Lake Bunyoni, partly because it absolutely poured down and some tents were a long way from the truck so recommend a waterproof/poncho and a daysack/camera bag cover. Also rained heavily at Musanze (gorilla trek). Waterproof trousers/gaiters worth taking if you have them, not just for the rain but also for the mud!
But...it was pretty hot in the day in Kenya and at Jinja so you need a hat, a small amount of sunscreen (60ml did for two of us because you are not outside very often even where it is hot). There are swimming pools at a couple of campsites (and you can pay to use the one at the hotel next to the campsite at Jinja) so maybe worth taking a cossie.
Very difficult to do laundry (really just Jinja) because there aren't many 2 night stops and it's often very rainy so nothing dries quickly - so you may need more clothes than you think.
Probably need to have "safari" colours on gorilla trek but the rest of the time it doesn't matter.
Plugs - UK on truck and in Kenya (Masai Mara tented camp)/Uganda (Lake Bunyoni and Jinja tented camps); but you need 2 pin plugs for the 3 nights in Rwanda. Take plenty of spare batteries - the truck can only charge stuff when it's been running for an hour and a half.
The locker system is a pain so you need small bags which you can use to transport stuff to and from the tent without repacking your entire bag/locker. Also a decent size padlock.
Shopping - not many opportunities so if you see something you like, buy it! big craft stalls en route to/from the Masai Mara but early in the trip and only a v quick stop; one supermarket sold postcards; souvenir shops in Jinja but only if you are not doing an all day activity and get a cab there or scrounge a lift if the truck; craft shops at the Equator inc one for children's charity; stalls at end of gorilla trek but not guaranteed to have time there. If you need stamps there is a post office in Jinja (but see above - most people won't actually go into town) and Musanze but it's 20-30 min's walk from the hotel.
Mozzie spray - there were a few about so worth taking a can but you don't need bucketloads. Also some After Bite - the few bites we did get were pretty itchy!
Toiletries - most campsites had hand soap by the basins, and the crew set up soap and hand basin with water before every meal, but you do need shower gel/shampoo, and antibacterial hand gel for times where there is no soap or you are just eating snacks. A couple of campsites didn't have showers. You need to take a toilet roll (possibly a 2nd in case of emergency, and immodium and something less fierce like diocalm, but only a couple of people on our trip got sick)
Camping stuff - definitely need a head torch, a pillow, quick dry towel and earplugs.