No, it's not about food. It is very idiomatic and is about preferences or likes. (1) 'Do whatever floats your boat' = 'Do want YOU want' (2) A:You want to see a movie or go to a restaurant? B: 'Whatever floats your boat' = 'Whatever YOU prefer' (3) 'Studying doesn't really float my boat much' = 'I don't really care for studying' Some more explanations here: https://www.urbandictionary.com/define.php?term=whatever%20floats%20your%20boat

Thanks Mr. Chris

It's means whatever you like or your personal taste. For example: "You can have chips or mash with your sausage; whatever floats your boat." And no, it's not just about food. It's for general preference.