Clarke Boltless Shelving Unit

 These are a Clarke’s branded product available from Machine Mart, but many other companies offer similar boltless construction shelving units. They are available in a mind boggling range of sizes, colours and weight capacities, and most can either be assembled as a single, tall shelf unit or as two smaller units that can perform double duty as shelf / workbench as required.
The units pictured are from the lighter capacity end of the range. They’re a little fiddly to assemble if you’re doing them on your own, but it’s doable and the only tools you may need are a rubber mallet to tap the pieces in place and a flat bladed screwdriver to help bend up the retaining tabs on the shelf cross braces. Once fully assembled, they’re study enough.
These have mdf shelves, which will be fine in the relative dry atmosphere of a garage, but I also have a set in the temporary garage (tent!), It’ll be interesting to see how the mdf shelves perform over winter in a much damper environment. (They warped, which I pretty much expected them to do. But they still hold stuff!)
The units used in the tent were a wider, more robust model as I wanted them to form a workbench suitable for my fibreglass work. To make them more rigid on the uneven floor of the tent, I joined the two units by adding a 9mm thick OSB sheet across the back - which also has the advantage of stopping stuff falling off the back of the units.
I would have taken a picture of these as well, but they’re currently buried under a mountain of junk and I don’t want to show just how untidy my workspace is, or spend time outside in the cold tidying them up! I assembled both sets as low shelf units / workbenches, so I can’t comment on their rigidity as a full-height unit. As mentioned at the start, similar units are available under various brand names, so it’s a case of deciding on what your size requirements are and then shopping around to get the best deal.