To make great sandwiches, it is all about the bread, the mains, and the condiments.
The corporate side of food has done everything possible to cheapen all condiments to maximize profit but allow funding for advertising to convince consumers to buy.
The store should make a deal with a local bread maker to have fresh, extraordinary bread delivered to the store daily. If that is not possible, the store should start thinking about setting up a small bakery operation. If you are making bread, you are turning pennies into dollars.
Meat or vegetable, mains have two jobs: big on taste and big on health.
Meats should be non-industrial and big, forward-flavour meats, preferably cured (though a steak sandwich freshly made is great in its own right).. The absolutely famous sustainable black ham from Spain is so amazing that Qualifirst is bringing it into Canada.
Vegetables, slice up peppers and other assorted veggies cut into long strips, shower with an excellent olive oil, dust with a higher quality of pepper, a little salt, and roast broil them. Cool, place in sealed containers to layer in a sandwich. Strips of Zucchini, peppers, carrot, the list is endless. Important to cut them to make large slices.
Cheese is special enough to have its own category. Here you want non-industrial cheese, and not that industrial crap sold with advertising. Emmental is a great raw milk cheese where the Swiss have fought to maintain the traditional quality.
This is where the rubber hits the road, making and breaking a sandwich. I am famous for my sandwiches because I understand the role condiments play. First rule is get rid of the industrial sauces and spreads that have been so manipulated that their production is more chemistry than food production. My make-or-break condiment list is:
Cornichon (the real ones. I slice them length-wise and layer in a sandwich)
Dijon Mustard (the big one in the reusable preserve jar made with white wine vinegar)
Dijon Grainy Mustard (link) also in the reusable preserve jar (half-cracked to allow the flavour to leave the seeds.
Olive oil (Surprise! lose the butter and sprinkle a little olive oil on the bread)
Black Pepper freshly crushed with a mortar and pestle (or grinder)
Black Garlic (link) spread like butter is rich in taste, moving the boundaries of great taste sideways.
Purple mustard has been described by culinary experts as gastronomic crack, and been around for over 400 years. Use sparingly.
Mayo … but not just any mayo. YUZU Mayo (!!) with NO MSG. The lemon notes from the Yuzu make this a step up from the industrial mayo sold these days in stores.
Spice selections to sprinkle very sparingly on the humid condiment (such as mustard or Yuzu Mayo) allows an artistic sandwich maker to move the goalposts of flavour. I will often mix real Oregano and Savory with the Dijon the night before to allow the flavours to blend, then use that on the sandwiches.