I like the "doing something for charity" suggestion. You'll get out, you'll meet new people, and you'll give back to the community.
Hey, get a group together and go over to the local food bank!
Or take a day trip... pick a spot you've never been, get in the car and go there.
Call or email an old friend you haven't seen in a while, and get together for coffee.
There are endless possibilities, even on a tight budget.