reply it in your way......
"Nothing much" or "Things and stuff".
I would answer with how I feel. Like "I am fine/not fine, how are you?" :-).
I would say "Not much, you?" or "same old, you." "Same old" as in "same old thing."
fine,what about u?
The following might seem a bit weird to you, but, this is a slight mix of how we talk naturally around where I live and well... "proper" English.
Nae/No' much at all really, wha' bout you/yersel'?
Not a lot, you?
No' an awful lot.
or if you're asking it in a how are you manner
Aye, am no/nae too bad.
and for those silly moments