Try this simple but really good tuna salad:
chop or dice (not too finely) a carrot, celery and some onion (red onion is good, or scallion greens are another option) and if they';re in season, cut up a tomato too
Mix tuna and the vegetables with good mayonnaise (you can add a little lemon for nicer flavor).
It lasts a couple of days. The crunch makes it much nicer.
Soft bread or crusty rolls.
If you have salame, prosciutto, mortadella, sharp cheese, you can put in one or more of those making sure you have the sharp cheese with them. Add those jarred "pepperoncini" - small green long thin peppers, drained (take of the stem and squeeze out the brine. I always liked this in a toasted pita. Crusty rolls are good too. Soft bread is not really suitable.
If you have leftover chicken, cut it up in cubes.
Chop celery (and if you like, carrot, onion) and mix with chicken, lemon juice, curry and raisins . Especially nice on a soft whole wheat bread.
sliced chicken and avocado
spread bread with mayonnaise, lay chicken slices on top, lettuce, a few slices of avocado
spread nice crispy french or italian bread generously with butter. Put halved radishes on top, salt and pepper. If you really must, add some brie.
long italian roll. mixed cold cuts including mortadella (mortadella and salame is good) and some provolone, then mix tomatoes, dill pickles, onion, pepperoncini if you like, and salt and pepper and origano and a little oil. spread over the whole thing. (This is one of the great american inventions of displaced italians who found themselved surrounded by abundance!) Italians in italy balk at the idea of more than one kind of cold cut in a sandwich.
I don;t like it, but my husband seems to love it. Large, thick slices of artisan bread, make a frittata, which can be leftover from supper, with the usual zucchine and onion, or better, artichokes and onion, or peppers and onion or just onion, and put it with all the oil of the cooking between the bread. (You should make the sandwich when you make the frittata, that is, the night before). They say the flavor of the oil flavors the bread and is even better sitting there overnight. If you like frittata you should like this. (I am prejudiced against it, i ate too much frittata and too much minestrone my first years here as a very poor student and i would be glad never to see either of them again!)
also i recommend trying various crispy vegetables in your sandwiches. Sliced cucumber, red bell pepper, radishes, etc can make a cheese sandwich more interesting.
avocado goes well with a lot of ingredients besides chicken. Try your ham and cheese with pickles, like bread and butter pickles. Try it with butter on crispy bread.
try using hummus in a sandwich - either alone with cucumber and/or other vegetables, or as a spread with other fillings.
"Siduri said, 'Gilgamesh, where are you roaming? You will never find the eternal life that you seek...Savour your food, make each of your days a delight, ... let music and dancing fill your house, love the child who holds you by the hand and give your wife pleasure in your embrace.'"