Okay, it’s sorta a poll (but I don’t know how to make them) but it’s about food, so I dunno?
Inspired by an argument with my sister (who is definitely a wacko)
What do you choose to put on a bologna sandwich? I’m talking here about things like flavorings/condiments, not whether you add additional ingredients like cheese or lettuce or tomatoes or whatever.
So:
Ketchup? Mustard? Butter? Mayo? Salsa? Chocolate syrup? Peanut butter?
I haven’t had a bologna sandwich since I was a kid, but back then (and I’m sure today, if I had one) it was yellow mustard.
Two slices of baloney, two singles of cheese-like substance, one slice of bread with mayo, the other with mustard.
Spicy mustard or mayo every once in a while. I haven’t had one in a long time.
It’s been more than 50 years for me. But I’d go with “plain.” I don’t put mustard or mayo on anything.
It’s been many years but even as a kid it was yellow mustard on rye.
Yellow mustard, American cheese, white bread. Anything fancier or better quality is almost missing the point.
I don’t like cold bologna, so I always had my bologna sandwiches grilled. And, like most of you, the last time I had one was probably 50 years ago.
With a grilled sandwich you can’t do too much, and since I’d have butter on the bread for the grilling, I wouldn’t need the mayo I’d typically put on a cold sandwich, so usually just mustard. Sometimes I’d add a slice of cheese before grilling.
Potato chips. Thats it. If I am going to indulge in a bologna sandwich I will have it kid style. White bread, bologna and potato chips alone with a Coke to wash it down.
With white bread, naturally. This is the only proper, acceptable bologna sandwich configuration.
With the caveat that, like most everyone else here, I haven’t had a bologna sandwich since I was like 11 years old – which was 30+ years ago now.
As someone upthread mentioned, rye bread is good, too. That’s what I’d use if it was handy, but mostly it was just white bread.
I eat bologna sandwiches every week, and it’s yellow cheese + Japanese mayo for me.
Until recently, I would have echoed some of the other posters and said that I haven’t had a bologna sandwich in many years (excepting mortadella, which is similar but a thing in itself, and even then, I only have it very occasionally).
But by coincidence, I’ve recently been making sandwiches involving bologna and my answer is that the most important ingredients in a bologna sandwich are … at least two other meats! Typically something like smoked ham and salami. The relative blandness of bologna and the stronger flavours of the others, in about equal amounts of each, creates a nice balance.
To this I’ll add Dijon mustard, tomato slices, a small amount of red onion, and a generous amount of lettuce (my favourite is an iceberg-romaine hybrid). The top slice of the sandwich will be buttered and slathered with mayo to complement the lettuce.
And since this a lot of stuff, it needs to be made on a soft bun – sliced bread is too flimsy. The result is something like an assorted sub. Those who like their bologna sandwiches relatively plain are probably just nostalgic for their childhood, but this is more of a “grown-up bologna sandwich”. I recommend it – it’s quite tasty! 
Mustard for me.
But the tricky part is finding really good bologna. What brands do y’all favor?
Another vote that baloney (screw that “Bologna” affectation) sandwiches are totally a kid thing. As such if I was going to have one I’m following this lead
So for me that’s ordinary white bread, mayo or ketchup not both, and baloney. Probably without cheese but if there is any, it’ll be Kraft American single slices.
I’m sure it’d be horrid today, but most of my true kid foods are.
ETA:
I now remember that as a hungry college dude I had a different baloney sandwich recipe.
Get a block of ordinary Kraft sharp cheddar and a package of sliced baloney. Neatly stack 3 - 6 slices of baloney on a plate alternating with a slice or two of the cheddar side by side in each layer. Pick up the finished stack and eat by hand with no bread or condiments.
Fast to make, filling, no mess, and no stupid hi carb zero nutrition bread.
Ketchup. Sometimes with a slice of real cheddar.
And only on white bread!
This. I rarely put mustard or mayo on anything, and certainly not on a baloney sandwich. No butter, no ketchup, no condiments at all.
Lots of mustard. Yellow will do, but I like a spicy brown or German mustard.
When I was a kid, I liked Miracle Whip on bologna sandwiches. Now I prefer yellow mustard. If I grill a bologna and cheese, however, Huy Fong Sriracha is awesome.
Currently doing mayo, white bread*, some leaf lettuce (sheapwr and easier than iceberg) and occasionally asking a tomato slice. Not going out to buy cheese* atm.
* means they are altered for my allergies, so no one tries to call me out or something.