I have a customer who is super cool, 'fit as many as you can over xx and bill me accordingly', so I'll fill up so many rows and bill him for an oddball quantity. But, the funny thing is, most of these are paired stickers for vehicles, same logo and all, but he's using an even number of them. Every once in a while he'll call complaining that jimbo must've screwed one up because he only has 3 left, get some more coming. I haven't pointed out to him that I probably ran an odd number at his request...
But really, I'd ship them out with the customers order, no use in holding onto overruns, just give them to the customer, or throw them out if he's a pita. All the vinyl drops though, they must be saved in a box under the table until it starts smelling oddly sweet...