Greetings
こんにちは
Konnichiwa
Hello (daytime).
おはようございます
Ohayō gozaimasu
Good morning (polite).
ありがとうございます
Arigatō gozaimasu
Thank you (polite).
お願いします
Onegaishimasu
Please (when making a request).
Social
すみません
Sumimasen
Excuse me / sorry / thanks — the all-purpose word you'll use constantly.
大丈夫です
Daijōbu desu
It's fine / I'm OK / no thanks — context does the work.
英語を話せますか？
Eigo o hanasemasu ka?
Do you speak English?
Daily life
いくらですか？
Ikura desu ka?
How much is it?
トイレはどこですか？
Toire wa doko desu ka?
Where's the toilet?
Food
お会計お願いします
O-kaikei onegaishimasu
The bill, please.
いただきます
Itadakimasu
'I gratefully receive' — said before eating.
Emergency
助けて！
Tasukete!
Help! — for emergencies.