Drinking tube clip - DIY alternative to the standard Platypus clip-on tube holder.
Flare tubes are discussed here
Guardian Safety Light - fitting one, and a small LED torch to a BA
Navigation Board - superb idea from Julian Patrick for organising charts/maps.
Paddle leash - article on making your own.
Paddles - making Splits / Jointing systems - discussion that includes reference to making your own splits using the Lendal sprung button system. There is an excellent photo-article on making a set of splits on unsponsored's blog - if you do this, I'd suggest making the cut off-centre so that when the spigot is fitted, the two halves are the same length. A mitre saw will produce a clean, square cut. Celtic Paddles (successor to Lendal) will supply spigots for their paddles, and 26/27/28 mm spigots and sprung buttons can be got from Whitewater or Up and Under.
Paddles - making Greenland paddles - excellent article from Thomas Yost's site (now defunct - on archive.org). Check out the Baker Brothers site [on archive.org] or (if you'd like a carbon fibre one), check out Duane Strosaker's page [on archive.org, sadly the photos have not been archived]. Shaman Kayaks is also well worth a look for the wonderful images of boats, paddles and other traditional goodies. Check out JulesT's description of how to make a greenland paddle. Qajaqusa.org have lots of information on making a West Greenland Paddle providing detailed instructions and a lot of background, history and tips on Greenland paddling technique - see also Matt Johnson's superb video based on making Chuck's Holst's design from that site.
Paddles - problems with Werners - stuck joints seems to be a common problem, this discussion has ideas on freeing them. At the other end of the spectrum, this discussion references worn joints on Werner paddles.
Shoulder Strap Mount for a Princeton Tec eco-flare (or other items) on a BA. The clip isn't sufficiently tight to actually grip anything, but is too wide and inflexible to go into the lash-points on a BA - this DIY offers a possible solution.
Stoves - diy - for background and ideas for making your own alcohol or wood stoves, see Zen Backpacking Stoves. Have a look here for some interesting ways of re-cycling your beer-cans into lightweight stoves.
Stoves - spare parts for - base-camp.co.uk seem to be a good source of bits for all sorts of old and new stoves, as well as bits for pressure lamps like Vapalux and Tilley. Needlesports hold stocks of spares for Primus, Trangia, Jetboil and MSR stoves as well, or can get them quickly. This eBay seller, Kibworth DIY, appears to have a range of washers and service kits for a variety of pressure lamps. As does Arty-pharty.
Tow lines - article on choosing, making and using a towline for a sea-kayak.
Trolley - excellent article by Mike Wood on making your own from an old golf trolley. As is this one on a Kayak Trolley (site being rebuilt - search for it) made from pvc pipe. This is a superb, simple and cheap DIY trolley. Here's one you you can make for £12.98.
Poop Tube (original link broken, just web search) - a neat way of packing out human waste, made from pvc pipe.
Storage solutions - illustrated article with a variety of ideas for storing sea kayaks.