I am one of the non sandwich eaters. Currently I am doing Slimming World, where effectively, I am allowed one slice of wholemeal bread a day, so sandwiches aren't really an option. I find it a bit odd that some people don't believe that some people don't like or don't want to eat cold sandwiches.
When I am at work in the office, or at home, I usually have leftovers for lunch. I batch cook a couple of meals at a time so almost always have leftovers available (usual stuff - soup, risotto, lasagne, cottage pie, bolognese, curry etc etc). Or easy stuff like omelettes, egg on toast etc if at home.
If eating lunch out, I will take a home made tuna pasta salad perhaps, but not in this heat.
If I need to buy something, my first choice would be something like Toby Carvery, or the occasional McDonalds or Greggs (pasty and soup - not a sandwich), or a cafe - a toasted sandwich and chips is far nicer than a cold sandwich and crisps IMO.
Only if I no other choice will I buy a sandwich, and then ideally I won't eat it until it has been out of the fridge for an hour or two because I hate fridge cold food - no taste and gives me stomach ache.
I do like some shop bought sandwiches, such as the M&S pastrami cheese and sauerkraut one, but at £4.50 a time, it's not an everyday purchase. Pret do a very nice halloumi and falafel one, but that's served hot, not cold.