Operative terms from the OP:

"Jump"
"Typical Sedan"

Nothing about taking an hour or more to cobble some sort of device from some sort of material, that may or may not put sufficient a charge on a flat and/or dead battery (two different things) for eventual conventional starting.

So: #4 copper cable. Less/not copper is a risk. Hot metal spatter or an explode lead-acid battery, or even a series of exploded AA batteries is no fun whatsoever.

Guys and gals: Give advice as if it were to a human being that you might possibly care about. And think about that advice as you give it. What you do for yourself and with only yourself at risk is fine. When you suggest that to another, own it and 100% of the potential consequences - even the possible limitations of the recipient.

Peter Wieck
Melrose Park, PA