Thanks very much.
To be clear, it's not that I think of salt/sodium as a fuel itself, but my 2 preferred on-bike sources of carbs (Gatorade and granola bars) both contain enough sodium that I'd avoid either of them off the bike. Given the amount of salt lost as sweat on a 3+ hour ride, I thought that I might get some additional leeway where a higher-sodium food might be OK.
My other favorite ride fuel (although slightly less convenient than granola bars) is Nutella sandwiches made with my own home-baked bread (which is much lower in sodium than store-bought bread) - I'll focus on that instead of the pre-packaged bars. I think I'll still use Gatorade for rides longer than 3 hours.