Whenever I eat Mcdonalds it's the coke that makes me feel guilty, and the super salty fries, the burger or nuggets I'm usually not that fussed about.

Salt isn't particularly bad unless you already have hypertension. There's a reason electrolyte (aka salt) dietary supplements like LMNT are becoming popular. Of course if you are already consuming lots of processed, salty foods you wouldn't need those supplements. But if you eat mostly whole foods, exercise regularly, and drink coffee you really do need to go out of your way to intake extra electrolytes.