Given that,
M=mass of the cylinder
F= applied force = 70 N
g = acceleration by gravity = 9.8 m/s²
the weight of the packet is:
w = m * g =58.8 N
This force must be "canceled out" by friction between the jaws of the vice and the cylinder. Each jaw will provide for half of the weight, so
(58.8 N) / 2 = (70 N) × µ
µ = 0.42