Some more recent history.
Here is a selection of sandwiches in an unknown London sandwich bar in 1972.
First thing I notice is the prices - from 10 pence to 15 pence! Then the obvious shortfall in the hygiene department. Sandwiches piled on top of each other with no coverings.
Then the ingredients. Some standards - unidentified cheese (probably mousetrap!), egg, chicken, ham. I remember liver sausage with great affection. Pressed veal surprised me. The bread looks like supermarket, sliced, Chorleywood processed blotting paper.
Moving on, I searched out a random menu (part of it above*) from a similar sandwich bar in London today. Prices have obviously risen astronomically. from around 10 pence to between £1.90 and £3.60. Hygiene regulations have improved and all sandwiches are now individually wrappped - unfortunately, usually in plastic.
But the biggest difference is in the ingredients. No longer anonymous 'bread' but a choice of focaccia, baps, baguettes or ciabatta. The cheese is no longer anonymous or singular; we have Emmental, cream cheese, brie, mozzarella beside the cheddar.
Other fillings unknown in the 1970s appear: Thai chicken, chicken tikka, tuna, prawns, smoked salmon, and of course, avocado.
I won't be here in another 50 years but I'd bet that the changes by then will be even more astounding.
* The full modern menu is here.