We have always proposed that you make your stock numbers as meaningful as possible and this is described in the manual provided with the software. You can change the stock number at any time and not have to worry about losing any history. The stock numbers can also be very long (50 characters) but be careful about this if you are tagging items, as we will truncate Stock Numbers on some labels because of available space.
There are lots of things you can do to make your stock numbers more meaningful, but you should think about what you are trying to get out of it before you do it. And you should have one primary person creating them otherwise you might find that you get people entering the information differently.
Some things that you might build into a stock number are:
Vendor Part Number
Item Code/Dept (like childrens books)
Since we use RetailEdge to do our business transactions, we actually do our stock numbers this way and set our Find By on the Sales Screen to "Stock Number" and not Description (which is what I think most people use). We can drill down to an item number or group of items pretty quickly this way.
Obviously if you go this route, you might have to scan your UPCs/ISB Numbers into the inventory UPC1 or UPC2 fields, but this is why we created them.