Riddle Me This #7 Answered

I posted this one last Saturday and now 'tis time for the answer! Even though one Gabe Mustin already guessed it! Curses. I'll get you next time.

But here is Riddle #7 one more time:

I am used for leaving
Overnight
A Long Weekend
Permanently
If small, I am overhead
If heavy, I am below
I am necessary only when you need me
Sit on me if I grow
Who am I?

Image courtesy of truemarmalade

A Suitcase.