Re: blowing up the bag may indeed have been the correct form of disposal
Oh $DIETY... that takes me back to my school days in the late 1960s and a classmate whose surname was something like Donague. His nickname had transitioned through Dongo, Pongo and finally settled onto Whiff - and, yes, he did live up to that name. He had been absent through illness on the last day of term. As I sat next to him, it became my job to tidy up the contents of his desk as well as my own. Unfortunately, he did have a habit of not eating the sandwiches that his mother would dutifully make for him each day. These he would store in the desk alongside his books (exercise, reference and hymn*). I seem to remember there were several day's worth of uneaten cheese sandwiches which, once the desk lid was opened, was accompanied by cries of horror as the pong wafted around the classroom.
* The hymn book he had kept especially to occasionally show us the exact page upon which, during one particular morning assembly, he had thrown up onto. On that fateful morning, I had been standing directly to his left but I'm glad to say that he had aimed his stomach contents mainly into the hymn book itself and partially to his right, much to the chagrin of the boy in that direction whose school blazer caught a good proportion of Whiff's deliverance.