One of the all time favorite garage ideas is to have a ping pong table. If you have a big garage or a tandem garage, you might have the room to put in a ping pong table which will be fun for the whole family. For a ping pong table, you need to have more room than you might think if you really want to be able to play a serious game.
Most garages aren't going to have the space on all sides that is needed for that "serious" game but you might have enough room for casual players. You probably will not have the garage ceiling be as high as you want either but that's OK as you can still have a lot of fun.
One of the main problems you might face is the proper lighting for ping pong. If you get a table with wheels, you might be able to play outside your garage if the whether is nice. But ping pong is meant to be played indoors without wind or breeze and so lighting then may become an issue. You might put some fluorescent lights in above the table and also you can open the garage doors for more light.
Please watch the video below of my new Robo-Pong 2040 that is a very slick machine that absolutely ROCKS for practicing.