I'd like to second what Darcy said above about feeling stronger and such from riding alone. I carry a cell phone, my wallet, and car keys, and wear a road id on my shoe (some folks already suggested those).

For me, riding alone on the country roads is like being a kid and getting that feeling of freedom and exploration (except I explore 20 or so miles at a time and am way more fit than when I was younger). And people on the roads and such tend to wave and smile, and I always feel good about that.