For me, it was something doughy with something fruity. A piece of apple pie would be the archetype.
I stopped eating anything at all after about 7 pm, and fairly quickly, my heartburn stopped. I’ve lost about 40 pounds since then, too, which hasn’t hurt. Now I can eat night time snacks again. Even an occasional late supper no longer bothers me.
I haven’t had a trace of heartburn in more than ten years.
KFC gravy. I don’t know why, but every time I eat it, I have heart burn.
I’ve been having problems with acid stomach a lot lately, too. Almost always in the middle of the night. I’ll wake up with my stomach feeling uncomfortably stretched, sit up and let out the grossest huge burp. I can’t figure out why this only happens when I’m sleeping. I get acid during the day, but not the gas buildup in my stomach. Does it have something to do with laying down?
I do know some triggers, mainly dairy and alcoholic beverages. It’s interesting that some say plain water gives them reflux. Does anybody know of any base-PH foods or beverages that might help? I hate eating Pepto tablets all the time because I seem to have heard that they cause you to lose bone calcium and I’m at the age where I need all the calcium in my bones I can get.
Does the younger crowd suffer as much as the elders?
Too much butter. I have this amazing brownie recipe that has a nearly criminal amount of butter in it, and I know they’ll kill me, but I can’t stop eating them. Also, citrus juice. I haven’t had orange juice in probably about 10 years, and while pineapple juice has only a slightly less severe result, sometimes I can’t help myself.
According to my mother, that means your baby will have red hair. She also said I have red hair because she ate a can of cherry pie filling every day while she was pregnant with me … but sees no possible connection between the pie filling and the heartburn. 
I would guess not, on average. I literally had no idea what heartburn actually felt like until my early 30s. I understood the word, but not the sensation.
Tea does it for me.
I had heartburn throughout my second pregnancy and had a redhead. However, I also craved fresh ground pepper and would put it on absolutely everything.
Sugar, and foods containing lots of sugar, especially if consumed close to bedtime.
I went off sugar completely for a few months and never had heartburn the whole time.
I also cut out snacks after dinner too, though.
Peanuts and eating after 7 pm or so.
I have zero heartburn from eating anything as long as I take omeprazole daily. I do still get reflux sometimes if I sleep on my right side. I try to sleep on my left side or back. If I don’t take the omeprazole I have constant low-grade heartburn, which doctor says would be worse long-term with the risk of esophageal ulcers/cancers than the risk of bone calcium loss. I take calcium supplements.