Couple of things I do.
I download movies to my IPod. I watch one each night in my tent, so that shortens the night by 2 hours. Usually the only way I watch movies.
I keep a detailed journal of my daily accounts. I've started drawing illustrations of my hikes, my campsites, and interesting stuff along the way. I figure this may help bring back memories years from now when I re read all of my journals. Plus its fun and eats up tent time.
I also take melatonin pills to help me sleep. If your unfamiliar with melatonin, its a natural hormone that your body produces to cause you to sleep. Its something you can buy at any grocery store, and not something you need a doctor or prescription for. And it really works. Of course you should always consult your doctor before taking pills, especially when you read about it on the internet. But it works great for me, and I usually sleep for 10 plus hours when I take them backpacking. Its not mind altering, it just relaxes you in a non drug way. And I'm fully rested for the next day of hiking.