Designing your backyard man cave with a theme in mind isn't mandatory, but it can really help tie things together and integrate it with your home. The hallmarks of a man cave are leisure and entertainment, so anything within this theme is sure to be a hit. Most indoor man caves typically include a large flat screen TV and maybe a gaming system of some kind. And depending on where you live, you could have these same manly luxuries outdoors as well. In places where rainfall isn't abundant, an outdoor TV is easy -- just mount it somewhere near the bar or cooking area and make sure it's covered. The same thing goes for the gaming system.
If you live in a part of the country that gets lots of summer thunderstorms, you can still go with an outdoor entertainment system; you'll just need to take more precautions. There are all kinds of outdoor TV cabinets and covers that will fit just about any theme you want to go with. You should also take the same precautions with your outdoor man cave games. Pool and ping pong tables aren't the best idea unless you have a fully covered area to work with. Think about incorporating some more outdoor-friendly games like horseshoes, volleyball or cornhole.