These lines are a mocking introduction to the protagonist of the poem, describing his race, social class, pedigree, wealth, and snobbery.
His surname brings to mind the Cabot family, part of the aristocracy of Boston. A well-known piece of doggerel suggests that “the Lowells talk only to Cabots, and the Cabots talk only to God”, meaning that the Cabots are the snootiest of all.
The whole name suggests John Cabot the explorer, who traded slaves in the Mediterranean and visited Newfoundland in 1497. The name thus evokes the colonial history of North America and the slave trade that brought the ancestors of the rioters to Chicago.
out of Wilma
Wilma is his mother. The phrase “out of” is the way that the descent of race horses is described, for example Triple Crown winner Justify is said to be “out of Stage Magic”. This is mocking the character’s preoccupation with pedigree.
once a Wycliffe
Wilma’s maiden name. The name suggests John Wycliffe, an important early Protestant theologian, so perhaps this is a nod at the ‘P’ in the character’s WASPishness.
This poetic concatenation perhaps refers to the colour of his shirt (white), suit (blue) and skin (pink).
below his golden hair,
Blond hair is associated with whiteness, and gold with wealth.
wrapped richly in right linen and right wool,
This alliterative line emphasizes the character’s wealth and snobbery. Linen shirts and wool suits are expensive, and the repetition of “right” suggests that Cabot looks down on ordinary people for wearing cheap cotton shirts and polyester suits.
almost forgot his Jaguar and Lake Bluff
Brooks continues to emphasize the character’s wealth and social background. Jaguar is a brand of expensive motor vehicles, and Lake Bluff is a wealthy white suburb of Chicago. Today Lake Bluff is 90% white and less than 1% black or African American, according to the U.S. Census.
The word “almost” is an extra little jab: the implication is that Cabot is so attached to his possessions and status that even the imminent threat of injury or death can’t make him forget them.