The point of MMM is perspective. Establish pride in living and spending like a badass and it's not starvation, it's growing satisfaction.
Why a gas-powered boat? What about a canoe or a kayak?
Can you get the same car used? Can you get past feeling unsafe in smaller vehicles? Mid-size sedans are actually safer than SUVs, generally.
Ultimately, what are you sacrificing, and do you want to sacrifice that thing? If you're FI 1% slower because you buy a tank of gas occasionally and that really makes you happy, you'll probably be ok. If you're spending your last 10 bucks on a boat you seldom use and you're underwater on your car and credit cards are late, the boat's a terrible idea. Ultimately, your goal isn't to cut out whatever you like that costs money. It's to evaluate, for example, in the case of the boat:
How much does this cost?
How much of a sacrifice is the cost, vs not having the thing?
Can I spend this much money acquiring more happiness for the same price, or more of the same happiness for a longer time for the same price?
The point is to change your perspective, not be miserable. Where you choose not to change perspective, don't sweat it too much - you can't succeed with frugality if you're miserable over it.