6:59 a.m. on July 29, 2010 (EDT)
I think There are a few basics that need to be fulfilled - if that ends up as ultralight so much the better - but the basics vary with the season and the circumstances. In a very dry climate you just can't travel very light as you need to carry all your water, in very cold climate you need a lot of weather protection, lots of food, and fuel, and so on.
Since a motorbike accident that nearly cost my life twenty years ago I am not a good trekker any more, so we, the wife and I, tend to go by Klepper kayak nowadays, thus the weight is of less importance, but bulk surely is!
Inland:
Two Hennessy's Hammocks, a huge tarp, a MSR kerosene stove (white spirits is a bit hard to get hold of here), two small folding chairs/stools, two Thermarests (or similar, one each), two sleeping bags, cameras, water-resistant binoculars, rain gear, food, and wine, plus a repair kit (for the kayak and other things that might break), medical supply, mobile phone, VHF radio - if at sea.
At times the huge tarp, and the Hennessies, are replaced by a storm-proof tent - sometimes a small one, sometimes our Atlas, if we plan to stay longer in one spot. The chairs, or stools, are luxury items, but as you approach 60 years they become more and more essential :-)!
Also, some extra equipment for the kayak is essential if you plan to be on away on a longer expedition, like bilge pump, batteries, solar panel, water purification equipment, sail and mast, outrigger, fishing gear, et cetera.
It also happens, if we plan to stay a long time in one spot, that we bring two thermarests apiece - so much nicer for your back:-)!