Clothing / tents - repairs - try these folk - "Maintain", Units 1-3, Harker Industrial Units, Harker, Carlisle, Cumbria CA6 4DS - 01228-674410 - repairs and alterations to outdoor kit and lightweight tents. Also try Lancashire Sports Repairs. Rubberman provides an excellent, quick service. Scottish Mountain Gear in Edinburgh can repair tents, Goretex cags etc but are no longer a Kokatat approved repair centre. SystemX are also authorised Kokatat repairers. Hammond Dry Suits offer repairs.
Clothing - cleaning, maintaining and storing garments made from breathable fabrics - excellent advice on general care and storage from Kokatat. Additionally, don't store (or dry) kit with latex seals in a room with any electric motors - they produce ozone, and ozone damages rubber and latex.
Clothing - reproofing - Nixwax is supposed to be good. (Although the "wash in" proofing may damage latex seals - apparently)
Clothing - repair tape / material - discussion
DIY kit making - have a look here for some interesting ways of re-cycling your beer-cans into lightweight stoves, and designs for home-made tarps, shelters, tents and rucsacs to name just a few of the bits of outdoor kit you can make yourself.
Latex seals - repair / replacement - The excellent Delia Ellard has sadly had to close Canyon Gear. Rubberman provides an excellent, quick service. Trident offer a replacement service, and a DIY kit. Hammond Dry Suits offer repairs and seal replacement. AquaTek make a range of drysuits and offer a repair service. For a DIY solution, see this discussion which contains excellent pictures of how to do it. Kokatat provide a set of detailed instructions on how to replace seals (scroll down the page). Adrian Shanahan also provides an excellent article on replacing neck seals [on archive.org] on his blog. West Coast Diving in Ayr may offer latex repairs. Edinburgh Drysuit Repairs offer seal replacement and the like and would be convenient for the East Coasters.
Pogies - make your own. From WhiteWaterSlalom.Net
Tent light - how to convert an Osram Dot-It into a hanging light.