S & P is a must. But why do you think you don't use herbs?
Probably because I rarely make a sandwich from a recipe, and especially if it's not from a recipe, I see a sandwich as a very, very quick-prep meal: some bread, some jarred condiment, a piece of cheese, and a bit of meat, for example. The whole thing is ready to eat in less than five minutes.
Adding herbs (since I don't prep them ahead of time like I should) would mean, at the very least, giving them a quick rinse and a pat dry, and whatever else is needed. For basil, that's nothing, because that's all the prep that's needed, but for thyme (which is probably my favorite herb), it's a lot more labor-intensive, pulling all those little leaves off.
It's one of those sick jokes that Nature has played on me - my favorite herb is the one that I hate the most to prepare.
Now, I will add something that just occurred to me: I'm assuming (my mistake) that you meant
fresh herbs. I will definitely add dried herbs to a particular sandwich, just because it's no more difficult than salt and pepper. When I have a salami sandwich, for example, I'll usually splash a bit of olive oil on one piece of bread and shake some all-purpose Italian seasoning over it.