The feeder answers are SHOVEL, DAVID, OFFICE, SPADE, OVAL, and CRICKET. We need to use the operations described in the various cities to make these words into a chain starting with PUSH. What can we do?
We still haven't gotten anywhere from PUSH, but apparently we need to get from there to SHOVEL. We can get from PUSH to SHOVE with the Twin Cities operation, and from SHOVE to SHOVEL in Chicago. ("Obtain an elevated train" means "add an L.") This leaves Phoenix's "defrosting" rule, which we must apply to OFFICE. When you remove the ice from OFFICE, you get OFF.
So the missing words were SHOVE OFF.