Oh yeah, forgot to cover Reserves.
Reserve pilots show up at the normal show time and hang out with a reserve plane. If cargo is too heavy for the normal plane assigned to a run, then they might load the excess on the reserve plane and send it as well. Only this time you'll fly there, get unloaded, and then immediately fly back empty. If you launch on one of these you'll probably be home by lunch.
Reserves sometimes cover other carriers routes as well. If a route serviced by another company like Ameriflight or Gem Air overflows, the carrier (UPS, FedEx, or USPS) might opt to use our reserve to cover the excess. Also, if another company can't send aircraft because of maintenance issues or something, you might go instead and cover their entire day at their outstation.
And if one of our pilots calls in sick, you'll simply go cover his entire run is his assigned aircraft.
As a reserve many times you simply show up, watch everybody else load and fly away, and then go home. However, that happens less and less often as we approach peak season (which is Mid-November to Mid-January) and the cargo loads increase to overflowing more often.