Calculate the total area of all the rectangular sides of the chocolate pack.

The chocolate pack is a triangular prism. It has three rectangular sides.
The length of the prism is $8 \text{ cm}$.
The sides of the triangular base are $4.2 \text{ cm}$, $3 \text{ cm}$, and $3 \text{ cm}$.
Each rectangular side will have a length of $8 \text{ cm}$ and a width corresponding to one of the triangle's sides.

Area of the first rectangular side (length $8 \text{ cm}$, width $4.2 \text{ cm}$):

Area of the second rectangular side (length $8 \text{ cm}$, width $3 \text{ cm}$):

Area of the third rectangular side (length $8 \text{ cm}$, width $3 \text{ cm}$):

The total area of all the rectangular sides is $\boxed{\text{81.6 cm}^2}$.

1.1.2) Calculate the perimeter of one triangle in mm.

The sides of the triangular base are $4.2 \text{ cm}$, $3 \text{ cm}$, and $3 \text{ cm}$.

The perimeter is the sum of all side lengths.

Since $1 \text{ cm} = 10 \text{ mm}$:

The perimeter of one triangle is $\boxed{\text{102 mm}}$.