Edison, according to legend, patented the light bulb. (He actually patented an improved filament, and the screw-in base.) Once the thing exists, it is easy to trace the process back to the origin, just as it is easy to trace from the leaf of a tree back to the trunk at ground level.
Edison did not patent the thousands of experimental filament failures that he tested before reaching a viable consumer product. His task was to climb the tree and find one particular leaf.
The PB & J sandwich seems simple. All you had to do was add two ingredients together!
But you also had to not add any of the other possible sandwich ingredients. No lettuce. No tomato. No mayonnaise. No mustard. No ketchup. No roast beef. No jalapeno slices. No pickles. No cole slaw. You also had to pick the right variety of bread. Pumpernickel doesn't work out quite as well. Sliced bagel favors different sorts of sandwiches. Cornbread doesn't work at all.
You can't just permute every possible combination of sandwich-able foods and expect the good combinations to be obvious. But once identified, they are obvious in retrospect, thanks to a quirk of human psychology. It wouldn't have been obvious that phonograph needles could be made from peanuts, or that light bulb filaments could be made from bamboo until after inventors had done it for the first time. So don't confuse simplicity with obviousness.
The problem with patenting a particular sandwich, or any other type of food recipe, is enforceability. Once the recipe is known, you have no way of knowing whether unlicensed cooks are making your dish.
The fact that Disney is using RFID bracelets, on the other hand, is immediately discoverable and verifiable by anyone who visits their parks. Furthermore, they have pockets deep enough to afford even unreasonable license terms. The problem was not even technical. It has always been human acceptance. Stick an RFID on a hospital-style plastic band, and no one wants to wear it. Embed it in an exclusive park souvenir, and people will even pay extra for the privilege of having one.
The bracelet is how you get the guest to carry the same RFID tag for their entire visit without losing it, breaking it, or shorting it out. Previously, Disney has used paper tickets, hand stamps, biometrics readers, and mobile applications to manage guests, and they still had problems with loopholes, fraud, and innocent accidents.
If someone were able to patent a PB&J sandwich, somewhere like a Disney theme park might be one of the few places on the planet where its licensing could be enforced profitably. They cannot hide what they do, as anyone present could read a menu and watch a sampling of trays exiting the serving line, then figure out the numbers on a napkin.
This is exactly what the patent system was made for; so the little guy could have an incentive to invent without being crushed by a copycat with more clout. So he doesn't have to be the only person to pitch it. He only has to be the first to offer patent licensing terms.