Pitch in for gas.
In the Shuswap, where I live, many families own a boat. And a boat is fun. From May to September that is. But a boat is a year long expense, especially if you financed it.
And people who have boats are very generous in that they invite people who don’t have boats to join them for a day on the lake.
Recognize that boat ownership is an expensive proposition. So pitch in for gas. It’s the right thing to do. Just because you don’t have a boat, doesn’t mean you can recognize the expense of having one. If their expense if your opportunity, pay your fair share. And, while we’re at it, wear a life jacket.