Informal/Slang Greetings
Hello
Hi 
Hey
How are you?
How is it going?
How you going?(Australia)
How are you doing?
Nice to see you!
Long time no see

Very informal/Slang
What’s going on?
What’s happening?
What’s the story?
Story?
Whatsup?
Sup?
Yo/Yoyo
What’s the craic? (Ireland)
You alright fella/lad? (UK)(for men only)
Hiya!
Howya?
Goodbyes in English
Goodbye
Bye
Bye Bye
See you later
Seeya(informal)
Take it easy
I’m off
See you on Thursday
Until next time
Take care
Stay safe
I gotta go 
Later 
Catch you later