Or you can do what I just saw on my flight last week. Standard looking duffel bag for a carryon in front of me standing in the jetway. Duffel gets unzipped and a softside pet carrier with a little dog is pulled out and the other carryon items stuffed into the duffel. They bypassed the $125 fee and were definitely DYKWIA types sitting way back in Y.
What is the $125 fee really for?