For serious work I use a full size carbon fibre Manfrotto Carbon One 441 but at well over a kg with head I suspect you may be looking for something lighter.
For lightweight work I use a Joby Gorillapod. They have various models. You'd need either the SLR or the SLR Zoom (the Zoom has the advantage of being able to use a proper tripod ball and socket head making it easier to compose the shot). These are nice and light, and stable depending on how you place them, though I've never used one for exposures much longer than 1 sec. You can splay the legs out over a rock though for a pretty sturdy base.
You may like to use a bean bag if you cook stuff like rice on your camps. This would be super lightweight as most of it would be eaten after, though again with the restrictions of having to place it on rocks etc.
I've used a range of cheap tripods that come between these in the past, though not for night shots, and they're unlikely to be suitable. It's likely that Chris will come in here with some good suggestions.
