I believe we've already referred you to the gear lists on the home page of this site.
The articles there have lots of suggestions for saving a half-ounce here and a half-ounce there, which can add up to several pounds. Getting your base weight (18 lbs. isn't bad, though!) down another couple of pounds will give you more leeway on the food and water.
You've gotten a lot of great advice on nutrition, so I won't add much. I've found that nuts are an excellent source of nutrition, containing healthy fats. If you can find a source of soynuts (soybeans cooked and then roasted), those are great, too, as both a protein and fat source.
I've found that, for me, I stay better hydrated on slightly less water (i.e. the water I drink stays inside instead of going in one end and out the other
) by adding a little electrolyte mix to my drinking water. I use the mix at half the recommended strength. Individuals do differ, but it might be worth a try. In alpine areas of the west, there are very few places where you don't run across a water source every couple of hours or sooner. Lower elevations and desert, of course, are a different story. Drought conditions also make a difference. "Tanking up" (drinking your fill) at water sources may (again, individuals differ) let you carry less water between sources. I generally carry only a quart at a time, two quarts at the most, but I don't hike in the desert. Nor (for the sake of my dog) do I hike when it's really hot.