The license plate on Gunpowder's car - a Dodge Challenger - reads "2A4EVER" which stands for "2nd Amendment Forever".
Jaz Sinclair, who stars in the spin-off Gen V (2023), is on the computer screen at the Red River Institute as one of the orphans there. An easter egg to show where she comes from and her backstory.
Homelander mentions several fictitious TV channel and streaming services in the ad for his birthday special. One of them is Vought-Mundo a take on Telemundo, a channel dedicated to Latin American content.
When Hughie is at red river and he's looking at all the photos of kids with powers there is a glimpse Marie Moreau who is the new lead of the spin-off show Gen V (2023).
At actual NRA events, guns are of course not allowed.