Nouns modified by adverbs?
Solution 1:
Titles and headlines are rarely sentences and have their own grammar formed by traditional usage and the need to attract paying customers/buyers.
They usually have some connection with the item, article, book, song, etc. Their construction is often characterised by omissions. These omissions arise because of the lack of space - titles and headlines are usually printed in large letters on a page or label - and they need to be able to be read “at a glance” and be memorable.
"Suddenly Susan" seems to be a shortening of "[Everything was normal and then] suddenly, [there was] Susan!” where “[there was] Susan” = Susan suddenly appeared and changed everything.
"Purely Pickles" is a name that was chosen by someone, and the rule with names is there are no rules whatsoever. In this case, however, the root word “pure” has several nuances (i) entirely; only; nothing more than (ii) utterly (iii) unadulterated; (iv) clean; wholesome. Thus Purely Pickles says to the reader, “This jar contains only fresh healthy pickles and no additives or unwanted ingredients whatsoever.”
Purely modifies “contains” adverbially.
Compare
“A: You said that English was easy to learn…”
B: “Yes, but I said that purely because (= for no other reason than) you were about to give up.”
You Can thus understand “Purely Pickles” as “This contains nothing but pickles.” Or “We (i.e. the company) make only unadulterated pickles and nothing else.”