Check out the WaPack trail in Ashburnham, going into southern NH. Some of it is along roads, and water is spotty in built up areas, but its a nice hike. We did the 21 miles in 2 days. Lots of ridgelines, plenty of places to hang along them.
For quick overnights, I normally just head up to Mt. Watatic, and hike north along the trail. Once you pass the Binney Hill Pond (perfect place to fill up water bottles at the foot of the hill), and hike up to the ridgeline, its a nice view, and fairly easy hiking for an overnighter. Finding water on top of the ridge may be tricky though. I usually find a place to set up, then go back & fill a water bag. You CAN find water up on the ridge, you just need to search some. Views are amazing though-you wont be disappointed!