Chalk
.Iʹll chalk out your path for you—i.e. lay it down or plan it out as a carpenter or ship-builder plans out his work with a piece of chalk.
I can walk a chalk as well as you. I am no more drunk than you are. The allusion is to the ordeal on board ship of trying men suspected of drunkenness. They were required to walk along a line chalked on the deck, without deviating to the right or left.