Will  you have another piece of cheesecake?	
Mine's a half of lager

How's life treating you?	
I'm easy

How's it going?	
Don't mind if I do, thanks.

Would you like some more of this?	
It's all right, thanks.

I'm stuffed.	
Can't complain.

My round, I think. What are you all having?	
Not so bad.

Tuck in!	
That's very kind of you.

Let me get this.	
No, I insist. It's my treat.

Sweet OK?	
I'd prefer dry, if that's all right with everyone else.	

Anyone mind if I turn up the air con?	
Sure, go ahead.

Chinese or western?	
Mmm. Delicious!

I'll get this.	
So am I. I couldn't eat another morsel.
	
Answers

Chinese or western?
I'm easy.

How's life treating you?*
Can't complain.*
Not so bad.*

How's it going?*
Can't complain.*
Not so bad.*

Will  you have another piece of cheesecake?
Don't mind if I do, thanks.
It's all right, thanks.

Would you like some more of this?
Don't mind if I do, thanks.
It's all right, thanks.

My round, I think. What are you all having?
Mine's a half of lager.*
It's all right, thanks. (I'm all right, thanks)

Sweet OK?
I'd prefer dry, if that's all right with everyone else.

Anyone mind if I turn up the air con?
Sure, go ahead.

I'm stuffed.*
So am I. I couldn't eat another morsel.

Tuck in!*
Mmm. Delicious!

Let me get this / I'll get this.*
That's very kind of you.
No, I insist. It's my treat.

* Very informal expressions that would  normally be used by people who know each other quite well, or at least, feel fairly relaxed in each other's company.