As for Class 2 Gases, since all gases are generally the same degree of danger, there is no need to assign Packing Groups. Please refer to DGR 184.108.40.206.
There is no PG assigned also to Class 1 Explosives. Instead they are assigned a Compatibility Group of a single letter which helps transport purposes. (Refer DGR 3.1.4; Table 3.1.A)
Organic Peroxides in Div. 5.2 also do not have a PG. The use of packagings satisfying a PG II performance standards is mandatory. (Refer DGR 220.127.116.11)
Infectious substances of Div. 6.2 also do not have a PG. A different UN number and a different PSN is assigned to infectious substances resulting to fatal diseases, and to those causing curable illness. (Refer DGR 18.104.22.168.2.1; 22.214.171.124.2.2)
For radioactive material in Class 7, IAEA assigns categories (I-White, II-Yellow and III-Yellow) depending on the strength of radiation. (Refer DGR Table 10.5.C)