The local currency is the Hong Kong dollar (HK$). ATMs are widely available; international debit/credit cards are accepted in most places except budget Cantonese restaurants.
Hotels A HK$10 or HK$20 note for the porter at luxury hotels; gratuity for cleaning staff at your discretion.
Restaurants Most eateries, except very cheap places, impose a 10% to 15% service charge. At budget joints, just rounding off to the nearest HK$10 is fine.
Bars and cafes Not expected unless table service is provided, in which case 10% will often be automatically added to your bill.
Taxis Tips are never expected, but many people leave the small change.