The 2 Bob Seger tickets Carl holds, when telling Homer about the concert, are both for row C, seat 4.
The naval ship on which Ralph Wiggum attends summer camp (or a field trip sleepover) is shown as the 'USS [and then there's a large black block censoring the name of the ship]. This is a tongue in cheek nod to the American / societal trend of cancel-culture and 'historical' white male statue topplings and removals.