Vomiting
Watery, non-bloody diarrhea
Crampy/diffuse abdominal pain
Features that suggest non-viral etiology:
Bloody diarrhea (Salmonella, shigella)
RLQ pain (Yersinia, Entamoeba)
Recent antibiotics + copious, foul diarrhea (C. Diff)
Consumption of previously cooked/reheated foods (especially meats, mayonnaise, etc.)
Explosive, "rice-water" diarrhea (cholera)
bloating, really nasty flatus/stools (giardia)
Bloody diarrhea (Salmonella, shigella)
RLQ pain (Yersinia, Entamoeba)
Recent antibiotics + copious, foul diarrhea (C. Diff)
Consumption of previously cooked/reheated foods (especially meats, mayonnaise, etc.)
Explosive, "rice-water" diarrhea (cholera)
bloating, really nasty flatus/stools (giardia)
Viral gastroenteritis
Abdominal aortic aneurysm
Bacterial gastroenteritis
Aortocaval fistula
Acute gastroenteritis 
Acute gastroenteritis
Aortoenteric fisulta
Post-infectious irritable bowel syndrome