Are there any at-home remedies to cure an upset stomach?

I’ve been kind of ill since yesterday (in and out of the bathroom, not vomiting), and I don’t have any Imodium or OTC medicines. Quite frankly, I don’t even think medicines could help.

I think I might have eaten something that upset my stomach. Sundays, my boyfriend and I will go to Dunkin Donuts and get a breakfast sandwich and coffee. Last Sunday after we ate, I had an upset stomach but it didn’t last long. I was in the bathroom once and done. But this stomach ache is sticking around. It’s like anything I put in me wants to come out right away. =[

Anyway, are there any non-medicinal remedies you guys use to treat an upset stomach/diarrhea?