Chapter 1: Section 3: Page 24: Line 53-56 (338-341)

"Long as we have this windfall, let's go get us some root beer, and some of that 'Cracker Jack,' too. Say, what do you know! We're here! We're at the Fair!"

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"root beer"
I wonder what root beer tasted like in 1893? Root beer became a national phenomenon in 1876 at the Philadelphia Centennial Exhibition, commercialized by Charles Hires, most famous up until that point for having two plural names. Hires began bottling it in 1893 so maybe that's the root beer Miles is excited to drink.
    Don't misunderstand me and think I'm saying Charles Hires invented root beer. Obviously the white man stole the idea of root beer from Native Americans because isn't that one of the running themes of Miles and Lindsay's experience at the Fair? American colonists arrived on the shores of America and were, "I need a drink! What can we ferment here on these shores?!" And the Native Americans were all, "These sassafras roots are pretty good! And healthy too!" Then the colonists were all, "Give us that!" The Native Americans were all, "Hey, chill out! Plenty to go around, my limited number of weird white dudes from the sea! Let's be cool!" And the colonists were all, "Are you looking at me funny?! Why I outta. . . !" And then . . . WHAMMO! . . . root beer!
    You now know why I never got better than a C- on my oral reports.
    Anyway, I still don't know what root beer might have tasted like in 1893. But then, I don't even know how to describe the flavor of root beer in 2021! If somebody asked what it tasted like, I would have to say, "It tastes like root beer." So maybe I shouldn't stress about it too much, seeing as how there are so many different ways to make root beer.

I guess it tasted like roots and barks and herbs.

"Cracker Jack"
The snack that would eventually become Cracker Jack was possibly sold at the Chicago World's Fair by a pair of brothers who had come up with the concept of molasses on popped corn with peanuts. But if it was (and it's probable the idea of it being sold there is simply a marketing retcon) it was almost certainly not named Cracker Jack but probably just sold as "Candied Popcorn and Peanuts." So, yes, Miles and Lindsay could have partook of a molasses covered popped corn kernel with peanuts at the Fair which later became Cracker Jack. But would Miles have called them "Cracker Jack"? Pynchon places the name in quotes to suggest that it's not the officially designated name of the snack item, maybe just the way people refer to that particular treat. Perhaps it was already taking off to such an extent that people were simply describing it as a "crackerjack snack" to their buddies. But the name wasn't trademarked until 1896. So did Pynchon get this wrong?
    The only answer to that is "Did young boys in airships travel around the world on secret missions in 1893?" Pynchon's novels live in a hazy environment of historical accuracy, urban legend, pop culture, mass marketing, and speculative fiction. In other words, it makes a good story and a nice reference to have Miles suggest trying some 'Cracker Jack.' It's like a director having to have a kid wearing a Walkman in an 80s film.

"Say, what do you know! We're here! We're at the Fair!"
All the wild stuff happening around them and Miles doesn't really feel like he's at the Fair until he contemplates the enjoyable snacks of which they're going to partake. I fucking get it, Miles. You're my boy!