We are in this situation. No local family--family is all on the West Coast. I do wish we had things like Grandma's Sunday dinner or brunch with the cousins to do on the weekends and often it feels lonely that we don't. We also have an only child and my husband works a lot of weekends.
So what we do is we have enrolled our child in a lot of classes each weekend (two each morning such as swim class and soccer). After the classes we go out to brunch, preferably with friends. I have have worked hard to make a lot of friends and we get together with them often. Once or twice a month I entertain at home, hosting a family brunch or dinner with friends and their kids. We go to birthday parties on the weekends, playdates, events like festivals or fairs, day trips, and a few errands. All that fills up the weekend.
But there are many weekends where besides the classes, we have nothing planned. That's why we're doing the classes, so at least if we have no other plans, at least I know that we will get to socialize at the classes.
Holidays are also difficult because for various reasons (including distance) we don't celebrate holidays with family. We often travel for holidays, or invite friends for Friendsgiving, etc.