If you plan on staying in Hong Kong for at least a few days, then it may be worth it buying an Octopus Card – a value stored smart card – for riding train, bus, ferry, tram and for payments in supermarkets convenience stores and food chains.
Most of the Hong Kong residents have such a card, because it is just so convenient.
You will surely use Hong Kong’s MTR train when touring Hong Kong. So buy the Octopus Card at any of the MTR train station ticketing offices.
Initially, you pay HK$150 for an adult card, with HK$50 as the deposit. When you leave Hong Kong and return the card, you can have your deposit back, as well as the remaining value on the card.
You can later add up to HK$1000 to the card. A machine for checking your card balance is available at each MTR station. The remaining value also shows on the small screen on the turnstile when you exit a station.
A convenient way to recharge the Octopus Card (besides using the ticketing office or the recharging machine at each of the MTR stations) is go to the conveneince stores 7 Eleven or Circle K, which are many in Hong Kong. Give the staff your card and tell them the amount of money you want to recharge (minimum HK$50), hand them the money, and it is done! You will get a receipt when the process is completed.
You can find more info about Octopus Card here.