can an event have activities asssociated with it?
CiviCRM lets you create price sets, which can be used to create an event sign-up with all kinds of different selections, such as workshops in different time slots. You'd create a price set field for each time slot, and the field would be set up with as many options as you needed to choose from. There can be a price associated with each different selection, or they can be "free"/zero dollar, or some combination.