Mine is Sprite or 7-up. My mother always gave it to us when we were little. I don’t know if it actually works or if it’s just the placebo effect.
Beer. Seriously.
I’ve been feeling out of sorts since last night. Just had a beer. Stomach is doing better.
Warm milk mixed with a raw egg cracked and a teaspoon of white vinegar and salt, frothed up with a wire whisk.
Just the approach to my lips forces violent removal of stomach contents.
Ginger ale is a traditional drink for upset stomach. Ginger tea before that.
My mom gave me Vernors when I had an upset stomach as a kid. I normally don’t like ginger ale, but when I was sick, it tasted good and settled my stomach somehow. Could have been the placebo effect like you said.
Water. That’s about the only time I drink the stuff.
7-UP here too. I seriously believed in it as a kid. My mom was a nurse!
Add that to the fact we kept little soda in the house when I was small, so as well as being a cure-all it was a treat, worth being sick for!
Coke, or Ginger ale, depending on the situation. I choose Coke in tiny sips when I’m actively nauseous, while gingerale is more psychologically comforting on a generic upset stomach (even though ginger does settle a stomach, there’s so little of it in ginger ale I don’t think it does much).
Ginger ale with as much of the carbonation stirred out as possible. When I had morning sickness, my husband did the stirring in advance for me. 
Pickle brine. I’m one of those people for whom an acid-y stomach is actually a signal that I’m hypoacidic. So I go for the pickle jar and take a sniff. If it smells good, I take a sip. If it tastes good, I take a glug, and that usually fixes me right up.
If it smells or tastes awful, I put it away and make some basil or peppermint tea. If someone’s going to the store anyhow, I put in a request for ginger ale, but if not, it’s not worth the extra trip to go get it.
Maalox or Mylanta
For serious nausea, one or two glugs of Pepto-Bismol chased by Seven Up.
Edit: first recommended to me by my primary care doctor.
Tea, either regular black tea or an herbal tea. Celestial Seasonings has something called Sleepytime Tea, and it has many stomach soothing herbs in it, like spearmint. It’s also good for a cold.
Angustara (sp?)Bitters and soda, very strong does wonders for me. Also Fernet Branca about 50/50 mixed with Coke.
Capt
Buttermilk
I had Sprite/7-Up recommended to me by a doctor after I’d had a kidney stone and been violently sick.
Any [non alcoholic] fizzy drink that’s been allowed to go almost flat is good for an upset stomach. I get them a lot from the diabetes meds I’m on.
lemon/lime soft drink, just a little flat.
Flat Coke.
Usually selzer because that’s always around the house. If I’m out, I’ll pick up some diet ginger ale.
Milk.