As an example: I recently bought two one-way tickets from LaGuardia Airport to Miami International Airport for $36 each on an American card. Cheap, right? Well, that’s why they get to treat us like human cargo. We're flying back on Delta Basic Economy -- which doesn't charge for carry-on bags -- for $80 apiece. So for about the price of two Knicks tickets and beers, my girlfriend and I will be flying to Miami in the dead of winter. If there are two things New Yorkers can rely on in February, it's the weather being better in Miami and the Knicks being irrelevant.
United manages to bury the information even better than American does, but a terms and conditions page explains "MileagePlus Premier members, primary cardmembers of a qualifying MileagePlus credit card and Star Alliance Gold members are still allowed a full-sized carry-on bag." In short: if you don't have elite status, sign up for a United credit card and you can bring a carry-on bag for no extra charge on Basic Economy flights. As with American, you can check your first bag for free, too, and you get priority boarding.