my @trip =   ("Chicago", "Saint Looey", "Joplin", "OKC", "Amarillo", "
+Gallup",
                         "Flagstaff", "Winona", "Kingman", "Barstow", 
+"San Bernandino", "LA" );
map { printf  "%15s to %-15s\n", @trip[$_..$_+1]  } 0..$#trip-1;
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which emits:

        Chicago to Saint Looey    
    Saint Looey to Joplin         
         Joplin to OKC            
            OKC to Amarillo       
       Amarillo to Gallup         
         Gallup to Flagstaff      
      Flagstaff to Winona         
         Winona to Kingman        
        Kingman to Barstow        
        Barstow to San Bernandino 
 San Bernandino to LA
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If you did this often, you might want a pairs_overlapping function. Or, going with a generic version:

subsequence(length=>3, step=>1, list=>\@trip);
[download]

a function that returns an arbitrary list of adjacent elements, with an arbitrary step size.

As to the next bit, I think several good solutions have been shown by others.