It’s sort of sneaky, but you can take advantage of the fact that a few items, like strollers, car seats and some medical items, never get a fee for getting checked in order to avoid checked bag fees on your other stuff, writes the Money Crashers blog.
What he does is put the car seat for his child in a large duffel bag and then toss in a few other items below it. He’s never had trouble with it so far. You can’t just toss an oxygen mask in a regular piece of luggage along with your clothes and get a free checked bag out of it, but you can at least free up some space in your carry-on and maybe avoid at least one checked bag fee.
11 Tips for Avoiding Airline Checked Baggage Fees [Money Crashers]