$\textbf{Answer}$

Meat.

$\textbf{Note}$

This is a riddle. So the key is to focus on the keyword and ignore all the distractions. This person's height and shoe sizes are clearly not sufficient to determine his weight. Therefore, these two pieces of information must be distractions. Cross them out. The statement becomes "A clerk at a butcher shop ... what does he weigh?" which is a bit clearer and easier to solve.

The word "what" can also serve as a hint. Usually we shall say "how much" does he weigh?