Up until they switched over fully to wax wrappers in the 1956-57 time frame (and sporadically thereafter) Topps used to insert a premium offer and comic in their gum card packs. These inserts mostly appeared in five cent packs but in earlier times could occasionally be found in the penny versions. Many of the early wrappers were made of glassine, which is similar to wax paper it that it preserves and contains air and liquids such as grease but is not as durable. Glassine is also subject to staining, making it less than ideal for selling things such as baseball cards and gum. So an inner layer to assist the outer layer makes sense if you are selling gum cards. It makes even more sense to use it to sell some stuff.
Topps would use one-panels for the comics, as opposed to the panel by panel action of their earlier strips and of course Bazooka Joe. Here is one called Li'l Pat:
Sometimes the insert was blank and I'm not sure if that was just due to ink running out on a run or cost saving measures. Earlier penny wraps were really just premium offers but interesting nonetheless:
The best of the bunch though is one shown here previously that features Roy Campanella and has Roogie himself endorsing Bazooka in way of a movie starring some Brooklyn Dodgers called Roogie's Bump. The Bazooka Joe Comic is pretty nice too!