When i buy a package of 12 drumsticks or a jar of chicken livers, I plan weeks to eat them.
Don't use Pull-N-Pak bags for freezing of meat. In a pinch, you could freeze something for a week. Any longer than a week and you should use purpose made freezer storage bags from the supermarket.
Is it better to use glass food containers such as Pyrex
Pyrex is better than pull-n-pak, but not as good a freezer bags. Why not as good? With any hard container, you can have an airspace which will facilitate freezer burn. A well packed freezer storage bag would have minimal airspace, minimal freezer burn.
Are pull-n-pak bags appropriate for storing raw vegetables in fridge?
Yes, for short term storage (under 1 week in my book).
Overall: the problem with pull-n-pak bags is that they are highly permeable for gas, vapors and moisture as compared to freezer bags. Also, the thinness of a pull-n-pak bag makes it susceptible to tearing in the freezer. Freezer burn can occur. Flavors and odors could also transfer among frozen items.
Alternative: Bags made for packaging ice. They'll be almost as good as freezer storage bags, but less expensive.
Ice bags are also available on Amazon.