The Mainsail Tack is attached to the Gooseneck with a captive shackle. This way a reef can be made in the Mainsail very easily.
When taking a reef in the Mainsail, a line is tied to the Leech Cringle (the clew which is up where the reef is...) and this line is led through this eyebolt and to the jam cleat. It is then led forward along the Boom and used to lash the Leech Cringle to the Boom. This way one line is used for both outhaul and vertical tension along the leech. (This is one of those descriptions which makes more sense when you're working with the objects!)
The small black-and-orange line (1/8" Spyderline) is the Jib Downhaul. It really helps pull the Jib down all the way, as it can kite up in windy conditions (kind of like when one has shortened sail in a blow, and doesn't want the Jib suddenly filling again!)
One can also see the snap I use to hold the Upper Barrel Bolt in place while the Rudder Box is on the Transom. The blue-and-white line is the Rudder Downhaul line. Notice the jam cleat on the top of the Rudder Box. The line is a bit long, as I can loop it under the rudder when the rudder is raised, then jam it back in the jam cleat and hold the rudder off the ground when launching.
Below, one can see the Axe Handle more clearly. It makes a nice-feeling, strong Tiller. One can also see part of the modified Taff Rail.