We add part numbers for everything - this is handy when we have to make a repeat order down the road - we have the vendor info, the vendor part and price - and we track how many parts we buy.
Light bulbs for example - we use several different types, indoor, outdoor, daylight for production area, Florescent bulbs, emergency lights, all of these are expensed, non-inventory items but it makes it real easy to identify what bulb I need to buy.  For some misc items that I am never going to buy again I use MISC as a part number.  In transactions you can see the vendor info but not any part number information.  other examples of non-inventory items - For bathroom tissue I use BATHROOM TISSUE as a part number, but I can buy a variety of brands from different vendors depending on price.  For tie wraps that are used in our product that must be a certain brand that I need to have the vendor information in the system to ensure continuity and they are on a BOM but are so inexpensive that its not worth tracking, I use a 6 digit part number but it is also expensed in the GL and non inventory.
Hope this helps
Regards
Debra