If your mother ever made you follow the classic cure for diarrhea, known as the BRAT diet (bananas, rice, applesauce, and toast), she was actually onto something. Bananas contain beneficial soluble fiber, including inulin, a prebiotic that also promotes the growth of good bacteria in the gut. They also have the added benefit of potassium, which helps restore nutrients that you lose after all that time on the toilet.
As your system starts to settle down, you're going to want to build up your energy levels with some protein. Opt for cooked, skinless chicken, turkey, or lean steak, which can all help you avoid fatigue that can be yet another unfortunate side effect of diarrhea.