Hearing Double. Get one and you’ll have a very useful clue to all the other long answers with question-mark clues.
All are 3 words long with an “ordinary” word in the middle and the puns on the two ends.
I though the first one you come across (Souvenir from the Petrified Forest) was one of the hardest. The ones further down in the puzzle somewhat easier. So try seeing if you can get enough down clues crossing long across clues to get a foothold.
56-across is really a stretch by the way, though the clue is literally accurate.
A couple specific hints:
Not all “food that jiggles” is JELLO, though it might be gelatin
Tolkien trilogy to fans: Think text message abbreviation
Some salmon: another one that’s come up at least twice in the last week.
Qatari bigwig: “var.” means that it’s an unusual spelling of a very common (especially in xwords)
90-down: A pair of initials plus a word
Alaska Peninsula: No, not YUKON, nor is it the place they named a huge Chevy SUV after, but it’s close. It’ll help to realize that a “measure of purity” might also be used to seduce someone into being less than pure!