It's a standard Canadian wire designation, suitable for use in wet locations. Most service entrance conductors here are RW90 insulated.
Ideally you could sell the single conductor #8 or trade it in for some larger cable. Unfortunately it's not a very useful or sought after item.
With the number of colors you have you'd be limited to 120 Volt circuits, unless you have lots of the black. It takes 4 conductors to do a standard 120/240 subfeed. Parallel runs in this gauge is not acceptable. The feeding breakers are not designed to hold 2 wires anyway. As others have pointed out the voltage drop at this distance will probably limit you to 15-20 amps total load at your shop with the #8.
For this application I would probably recommend #2 TECK breakered at 60 amps, or 1/0 ACWU. These are both armored direct bury cables. That should be enough to run a medium size welder and lights, etc. (again I've given Canadian cable designations)
Mike