Here are some common expressions you are bound to hear / see / be able to use:

Selamat datang / WelcomeApa kabar? / How are you?
Selamat pagi / Good morning
Selamat siang / Good may
Selamat sore / Good afternoon
Selamat malam / Good evening
Selamat makan / Have a nice meal
Selamat bertamasya / Have a nice trip / holiday
Have a nice trip / goodbye (if someone is leaving)
Selamat jalan  / Goodbye (if you are leaving)

Selamat tinggal / Goodbye
Terima kasih / Thank you
Sama sama / Don’t mention it
Tidak terimah kasih / No thank you

Berapa harganya? / How much does it cost / what’s the price?
Mahal! / Expensive!
Murah! / Cheap
Boleh tawar? / Can I bargain?
Harga pas / Fixed price