Miscellaneous expenses (e.g. iPad giveaway, or Membership fees) and credits (e.g. partial booth service refund) for an event can be tracked under the [Misc. Expenses & Credits] tab of an event; this tab can be accessed via the extended menu on the event page tab strip.
Expenses entered under this tab will count towards the total actual costs of the Misc. Expenses line-item in the event-specific budget. Credit entries will show as negative amounts and will count against the total actual expenses for the event.