You just have to be creative...I have a pretty full shop in my garage and STILL have room to park 3 cars in the 3-car....
When I had to suck my 10x20 storage unit back into my garage I bought some overhaed racks and a bunch of cheap wall cabinets from Home Depot. They work really, really well. I also have used just about every bit of usable wall space.
The overheads do not interfere with the garage door. I have also been thinking about opening the roof in the small garage to gain access to the rafters for additional overhead storage, but as you can see I do everything with a closed garage.
The main garage right side, viewed from the kitchen door:
My accessible storage. Electronics and other goodies are in the cabinet. I keep all my camping gear and other things I use often on the rack shelves.
You can also see how I use most of the available wall space. The Cadillac usually sits in that space, but I think it's going to wind up being my daughter's, since she can't afford another car and the one she had burned up. All that junk on the floor is what I was storing in the car.
More overhead storage. I just pulled down the Christmas stuff. Usually it is packed to the ceiling.
This is my shop. Every bit of usable space is used. The open space is where I park my Jeep.
I cheat a little, though, since my garage is kinda unique. It's a 2+1, but instead of the side garage being detached, they are connected, creating a 15x6 dead space that was perfect for my workshop. Since we bought the house as new construction, I had the builders put an extra 100 amps on the wall there: 50 amps of 110 and 50 amps of 220.
Despite the fact that I have so much stuff in the garage, I can STILL fit 3 cars in my 3-car garage. I'm very proud of that.