The Acquired episode about Costco (https://www.acquired.fm/episodes/costco) claims they don't do loss leaders at all.

It would be illogical to make gasoline a "loss leader" because, surely, there are people who visit the gas station and then jet out of there without going anywhere else. A loss leader item is something that gets people in the door, puts their butt in a seat, and gets them to make a transaction that will include piling on other stuff. So if your Jumbo Jack is a loss leader, then you can charge $2.00 for sodas and $3.00 for French fries, and the same customer will probably also grab a $6 Oreo shake.

Someone who's filling up for gas may or may not go inside the Costco store proper. But the gasoline isn't going to influence their buying habits. If they "just need gas" that's all they'll get.

Conversely, I cannot see how a $1.50 hot dog is doing anything but losing money. It's a classic candidate for loss leader.