I find they'll add whatever you want.
It never fails when I'm waiting in line, though ...
Customer: I'll have a ham and cheese.
Maker: White, wheat, or flat bread?
Customer Uh ... white.
Maker: Okay. (cuts, sets bread on counter)
.... long stare and silence ....
Maker: What would you like on that?
Customer: ... HAM AND CHEESE.
Maker: (adds ham, slides over to cheese but does not add any)
.... more silence ....
Maker: What kind of cheese?
Customer: (stares for a moment) I don't know! Cheddar. Cheddar's good.
Maker: (adds cheddar)
.... more silence and staring ....
Maker: Anything else?
Customer: (throws up hands) Well gee, how about MAYO or MUSTARD or LETTUCE or a TOMATO or like STUFF THAT GOES ON A FREAKING HAM AND CHEESE SANDWICH!? WHY DO I HAVE TO TELL YOU HOW TO MAKE A HAM AND CHEESE SANDWICH? YOU WORK AT SUBWAY!!!
Maker: (adds mayo, mustard, lettuce, tomato) Anything else?
Customer: ARRRGH! NO! Nothing else! Just ring it up so I can get out of this STUPID PLACE!
Maker: (wraps sandwich) That'll be $5.95.
Every. Single. Time.
It really couldn't be that hard to have a certain number of "standard" sandwiches for people who request it. They design them for the commercials and menus. Obviously if someone orders chicken teriyaki, you should put teriyaki sauce on it. A meatball sub, yeah, they probably want sauce and mozzarella like you show on TV. Etc.