Typically most shops will do the cutouts in one piece. But don't feel that the cut out is yours since you purchased the top. They may give it to you, or it may be used for small splashes etc. Your purchasing a finished countertop not the slab and you typically don't get what is left over.
It would be very heavy to move around for a pastry slab.

Mine was one piece also. I asked if they could take the granite from the cut out for the cooktop and use it for the countertop in the powder room. They said it was no problem since I was buying the slab. They also made a cutting board and lazy susan for me without being asked. I just assumed the granite leftovers were mine since we were being charged for the slab.

In our case we were purchasing the whole slab (ours is soapstone). I forgot to ask for the remnants before the slab was cut. Fortunately when I called the fabricator went out and looked in the scrap heap and found a leftover piece (not the sink cutout) that was 45x15. Apparently that was the only piece of any size they could find. We had them edge the whole piece and are going to use it for the top of a console table we'll have built for our living room.

Thanks for your input, everyone. Wish I had thought about that cutout much sooner than I did! Maybe this will serve to help others who might find themselves in the same position.
Fiesta

My fabricators left me the sink cut-out (and I had a real big sink). I paid only for the counter, not the entire slab. But I don't know what to do with it. It's in the garage. Any ideas?

I got my sink cut-out because they cut it right in my kitchen. However it has some "cut" marks in itso it won't make a pretty pastry slab. I'm probably going to set it in my garden somewhere. My fabricator also imports stone and I didn't purchase it by the slab, just by the job.