I have a bunch of metal craftsman rails that I bought when on sale. You can usually buy the pair for $6 or something when on sale. I also have a few from Tekton I bought at flea market that work just as well. To be honest though, one of the best things I did was buy the 47 piece 3/8" SK set and the 51 piece 1/4" Gearwrench set. They both come in sturdy, plastic cases that snap closed, but the lids are also removable. So, I set them in my tool box without the lids on and grab as needed. Or, sometimes I grab the entire set and bring them under the hood/car or I can snap the lids back on and take them on the road with me. Plus they have all sockets (metric, sae, deep, shallow) extensions, ratchet and universal. That's way easier then grabbing different rails and ratchets, extensions, etc, but understand you already have sockets and what not so the rails are probably your best bet.
Below is pic of his I keep my 1/4" set in my chest.