The boring answer is meetings. Chapter 3 of High Output Management has a great treatment on the topic, and it covers both middle management and the executive level, including a timetable from one of Andy Grove's days. Here is a quote where he summarizes:

> As you can see, in a typical day of mine one can count some twenty-five separate activities in which I participated, mostly information-gathering and - giving, but also decision-making and nudging. You can also see that some two thirds of my time was spent in a meeting of one kind or another. Before you are horrified by how much time I spend in meetings, answer a question: which of the activities -- information-gathering, information-giving, decision-making, nudging, and being a role model—could I have performed outside a meeting? The answer is practically none. Meetings provide an occasion for managerial activities.