Do woodwork for lots of years. You'll be amazed at how your eye learns to detect scale and picks the right wrench out of a disorganised pile 
Anyone have an idea or two??? One can buy metal or plastic holders for drill bits, or for wrenches, but I can not find an after market holder for allen wrenches. Sure, I could buy a new set of wrenches that comes with a holder, but then what do I do with the 25 - 30 loose allens I already have