Kaylee's gray coveralls are worn in several episodes. They are long-sleeved with a snap closure.
More pictures after the break...
The above is from Jaynestown, like the next few:
She is wearing this tank underneath:
Screencaps from Shindig:
Screencap from Ariel:
Some screencaps from War Stories:
Screencaps from Trash:
And this shirt is being worn underneath here:
My Photobucket Album for Kaylee.
Serenifly Costumes site for Kaylee.