For small items, add drones and the last miles savings get big.

  Weight of a typical car: 4,000 lbs. 
  Weight of a typical delivery drone: 80 lbs. 
  Typical drone payload: 5 lbs.
  5 mile drone delivery: ~2 kWh
  5 mile car delivery: ~100 kWh

So the breakeven is ~50 such items in one order.