It may depend on where you are going. If you are backpacking in the midwest then you can take a tarp with no poles because there are always trees to tie off to. If you go out west it's a different story of course. When I go fast and light in the Ozarks I just bring a poncho/tarp and tie off to trees or use sticks that I find as poles. I also use it for rainwear so it does double duty -- further lightening my load.

Other that the tent and the lack of hydration system (already mentioned) this is a pretty respectable list.