Literal translation
and the little extra bit
Meaning
and a little more besides
Explanation
A little bit more, sometimes signaling an addition, sometimes, figuratively, marking pointed doubt, like a yeah, right. Lou chèchou denotes along the coast a small thing, a tiny amount, a word related to chèchi, the childish term for chickpea (which also gave chichi-frégi, the fried chickpea specialty). Figuratively, the underlying idea is that one more little something, meaning a lot, would still be needed for the thing to be believable.