Actually, I thought the OP had a pretty good grasp of American food for someone who, I presume, has never actually been here.
I’m going to throw out a few more suggestions/examples.
BREAKFAST:
What, nobody mentioned corn flakes? Invented in Battle Creek, Michigan. A bowl of corn flakes and milk - don’t let them sit long enough to get soggy! - a glass of orange juice, and a cup of coffee is typical lightweight American breakfast.
My in-laws are quite fond of cornbread broken up and mashed into a sort of porridge in buttermilk, but that’s more a southern thing than anywhere else. In fact, I’m not even sure it’s a breakfast food.
LUNCH:
As an alternative to the grilled cheese and tomato soup, I will suggest either a hot dog or hamburger.
Typical toppings for a hot dog would include mustard, pickle relish, and diced onion. Some regions add other stuff, such as sauerkraut or “sport peppers”, but the mustard/pickle relish/onion condiments are pretty much universally offered. Be warned - some people get VERY touchy about ketchup and 'dogs - personally, I’m in the no ketchup on hot dogs, nope, never camp. Traditional buns are white bread and very soft, although whole wheat are becoming more common. Poppy seeds are optional
Hamburger toppings are typically lettuce, tomato, and onion. Some people include pickles. Buns are also traditional soft white bread. Add a slice of melted cheese for a cheeseburger.
Both hot dogs and burgers are served with either french fries or potato chips (you folks in the UK call them “crisps”, if I recall). For a picnic, coleslaw and/or potato salad are common additions.
But for a typical American lunch pretty much any sandwich served with either a bowl of soup, or a bag of chips with maybe a piece of fruit (apple, banana, or orange) or a couple cookies is not uncommon. The key point here is that it’s items that would survive traveling several hours in a brown paper bag (except for the soup).
Oh - and don’t forget peanut butter and jelly sandwich on white bread. As American as grilled cheese.
APPETIZERS:
a sort of before-meal snack you feed the hungry hordes to prevent and assault on the kitchen - come in a variety choices. Appetizers may be offered in between actual meals as a snack at a prolonged gathering such as a family event, between lunch and dinner for example. They also make an appearance at such places as Super Bowl and New Year’s parties where festivities may continue for hours and are not centered around a formal meal.
In my family, a typical one was a tray of sliced raw vegetables such as carrots, celery, cucumber and green onions along with a dip. Broccoli florets and pieces of cauliflower are two others I recall, along with cherry tomatoes. I’m not a fan of dips, so I hope someone else who is an afficiando can chime in with suggestions.
Another appetizer is the cheese and sausage tray. This is cubes of cheese (any variety allowed, although American, cheddar, and Swiss are common) along with slices/cubes of sausage (pepperoni, summer sausage, and so forth) served along with a variety of crackers. A small container of toothpicks is often provided, allowing guests to spear the cheese and sausage bits without touching them with actual fingers and using the little wooden splinters to transfer the cheese/meat to crackers prior to consumption.
Then there is the pickle/olive tray. That’s, uh, well, it’s an assortment of pickles and olives, along with spearing toothpicks. Another appetizer is the nut assortment (self explanatory) which may be as simple as opening a can of assorted nuts, or arranging different varieties of nuts into their own little groups. There is also the chip bowl (frequently combined with the raw vegee tray so you can use the same dip(s) on both) and the pretzel assortment
There there is the melon ball salad. That’s a mixture of balls scooped out of various melons. A traditional combination would be watermelon, cantaloupe, and honeydew. If you want to get fancy, carve the watermelon rind into a basket shape and fill it with the mixed balls. If you don’t have a melon baller (a little metal scoop specifically for making this sort of thing) cutting the melons into cubes would be OK, too.
Get an event with 12 or more people you might see all of the above.
DINNER:
“Starter” is usually a salad, if I understand the term correctly. Iceberg lettuce and tomato wedges are the most common base, with the addition of carrots, celery, onions and cucumber being common. Another common one is the Cesear salad, which is romaine lettuce, croutons, and grated cheese with Ceaser dressing, with anchovies optional.
There are a couple of possible main courses. Roast beef and mashed potatoes is one. You must have gravy for the mashed potatoes. Usually served with another vegetable such a green beans or peas-and-carrots. Bread and butter, or rolls and butter, are also frequently served.
Another entree - and this one is very traditional - is steak and potato. The steak is, ideally, grilled. Potatoes are either baked (sour cream, butter, onions, etc. are all frequent toppings although it also perfectly acceptable to opt for just a dusting of salt) and ideally Idaho baking potatoes, or they are thick fries/chips. Grilled mushrooms and/or onions are options for topping the steak but certainly not required. Steak sauce is another option. The steaks should be thick. An additional vegetable is also optional, and may be green beans (again), cooked carrots, yellow corn kernels, peas, and so on but it would be rare to see more than one. Bread of some sort - rolls, biscuts, thick slices, etc. - should be served along with butter.
Meatloaf, mashed-potatoes-and-gravy, plus another vegetable (see roast beef and steak for options), bread and butter.
Chicken - and you can get into a lot of regional variations. The chicken can be baked or fried. For a typical meal you would have mashed potatoes OR stuffing - it would have to be a big event such as Thanksgiving to have both at the same time - and a vegetable. Coleslaw seems more common with friend chicken and cooked vegetable with baked. Serve with bread/biscuits/rolls and butter. Or with cornbread. The southern variation is to have cooked greens. Turnip and collard greens have already been mentioned but nothing says southern home cooking like poke sallet – but it’s very unlikely you’d be able to get that in the UK. Hell, I can’t even get it where I live (in fact, I’ve only had it at the mother-in-law’s house). Creamed spinach is another option.
Tuna noodle casserole (or “hot dish” if you’re from Minnesota and/or Lutheran) - there are a million variations on this one, but the base is a can of tuna, a can of condensed cream of mushroom soup, a can of mixed vegetables, and a bag of egg noodles. This has already been mentioned.
DESSERT:
Pie - common varieties are apple, cherry, pumpkin (traditional at Thanksgiving), and pecan. A scoop of ice cream on top (usually vanilla) makes it pie a la mode. For a sort of weird variation there is “mock apple pie” where the main filling is Ritz crackers and it does taste sort of like apple pie.
Cake - a two layer cake with icing, either yellow cake/vanilla icing or chocolate cake and icing.
Brownies - with or without ice cream on top.
Ice cream sundae - a scoop or two (or three) of vanilla ice cream with chocolate sauce poured on top, chopped nuts, and a cherry on top. If the chocolate sauce is heated prior to pouring it’s a hot fudge sundae. A banana split is basically a peeled banana split lengthwise with a chocolate sundae built on top of it.
Jello/Jello salad - Jello is the brand name of a flavored gelatin. Either plain jello molded into a particular shape, or jello molded into a shape with bits of fruit floating inside it (apple and banana are common choices but I’ve seen others including strawberries and grapes), or jello layered with either alternating flavors of jello or jello/pudding layers. (The latter is achieved by mixing one layer, pouring it into clear glasses, allowing it to chill/harden, then mixing the next layer and pouring/chilling, etc.) A triple layer of red and blue jello separated by either clear or a layer of vanilla (for white) topped with whipped cream and colored sprinkles would make a suitable dessert for a Fourth of July/Independence Day picnic. When I was younger and mother let me run rampant in the kitchen I created some rather impressive rainbow layering with jello.