What is the nature of your dissatisfaction with that post?
"bells and whistles" are extra embellishments or features on something
Sainsburys is a ubiquitous national chain of supermarkets, maj works at one.
Puffer is one of these:
Trackies or jogging bottoms are "tracksuit/running pants"
"went hard" from "[to] go hard" - doing something to its fullest
obvo = obvious
mong = someone underdeveloped mentally, retarded or otherwise intellectually challenged. From "mongoloid" which used to be a harsh word for someone with Down's syndrome but can be used more generally. See also: spack or spazz.