Grilled cheese. BLTs are good too.
What I have most days is roast beef and cheese (usually pepperjack or harvarti) on a sourdough roll with may and mustard.
I was just about to post to say that one could reduce it to buttering just half the slice and inserting it along the reverse of the buttered/unbuttered axis. Biting down would automatically fold the bread as well. 
Tomato and blue cheese on toast, broiled
Bacon, tomato and mayo on toast
Meatloaf and ketchup
Oh, that reminds me (if open-faced bread-vehicled items count) – English muffin pizzas from under the broiler. Muffin half, Prego, mozzarella only.
Damn that sounds good. I have Eggos in the freezer…
For me it’s peanut butter and strawberry margarita jam (which I make myself).
A close second would be Braunschweiger and mustard, or perhaps a smoked sausage patty on a biscuit with garlic jelly.
Leftover cold bacon and butter on white bread.
Extra crunchy peanut butter on the heels of white or wheat bread.
Liverwurst alone on white bread or crusty french bread.
Fresh tomatoes and basil from my garden on toasted baguette slices with fresh mozzarella and olive oil and balsamic vinegar.
For me: beef bologna, Kraft single, iceberg lettuce (middle of the head: greenish but not limp) and Miracle Whip* on Roman Meal bread.
It’s so very white and mid-western. It’s the first sandwich I learned to make after a grilled cheese. I can’t buy Roman Meal anymore, but a sandwich made with a close approximation will instantly take me back to my seven year old self parked in front of the TV on Saturday morning. Watching cartoons, neck craned back (I sat way too close) and hoping CBS wouldn’t preempt the Dukes of Hazzard rerun with some stupid sport or something.
Good? Maybe not. Favorite? Absolutely. One bite and I’m thirty years younger, waiting for Bo and Luke (and Daisy!) to do their thing.**
*Chill. I’ve long since been converted to mayo, but this sandwich requires the other thing…
**Dynamite arrows. Goddamn, but did I love the dynamite arrows.
Cream cheese and apricot preserves on the whitest fluffiest bread possible.
Completely devoid of anything resembling nutrition, but it’s sort of a sandwich version of a kolacky, so it’s amazing.
Ham and jam (apricot is good, but any kind, really) on buttered bread. Maybe with a slice of Swiss cheese. I basically lived on this for a year in Czechoslovakia.
BLT.
I only get them eating out; I’ve never actually made one for myself because I’m always missing at least one of the key ingredients.
Costco canned chicken, best foods, diced celery, sweet relish, celery salt on miners sourdough…
slurp!!!
Cucumbers and cheddar on white or wheat bread.
Pumpernickel with butter and sliced radishes. Open faced, sprinkled with salt.
The one sandwich that I can make that literally makes my mouth start watering on cue, the minute I think of it is very simple:
White bread
Miracle whip or mayonnaise
Cheddar Cheese (Or American if I must)
My all time favorite sandwich has just three ingredients: Bologna, American cheese, and in-season tomato slices on toasted white bread.
And if we’re not counting condiments as ingredients, add yellow mustard, salt & pepper.
mmym
My easiest and most comforting go-to is scrambled egg on toasted Pepperidge Farm white bread with mayo, salt and pepper. We always have all of those ingredients in the house.
Hungry now. For summer vegetables, especially…I want REAL tomatoes!
I forgot about Eggo waffles–I do love a waffle with crunchy peanut butter and a little drizzle of honey. Completely different than pb and honey on bread.
grilled pb&JAM
white/baloney/butter/mustard
white/sliced cheese in a micro. watch it. stop when it looks good.
white/sliced cucumber or potato chips and any lunch meat and cheese.
Colby cheese on fresh ciabatta roll.
Add fresh tomato in season.
Fresh tomato, cheddar cheese, butter and mayo, on a crusty roll.
I haven’t made it in a while but I used to like braunschweiger, cream cheese and onion on burnt toast.
Cheddar and pesto on wholemeal.