Snacks, that's exactly what I used to do with DD. I just thought it might be easier, especially if you might have to get out and fix your first child something to eat or drink. But then again, you could just leave the baby in the car for a couple of minutes, look after the toddler, get her settled, then get the baby out of the car and feed to sleep...
By the way, Snacklet's due date is my DD1's birth date!
Saša