When Kenny reaches heaven, you hear "Open the gate!" followed by a higher-pitched "Open the gate!", mimcing Max arriving at the oil refinery for the first time.
An Angel says to Kenny "We are outnumbered and in need of someone who can bring everyone down, basically Kenny, you are Keanu Reeves", a reference to Keanu's character Neo in the Matrix who did just that.
An Angel watches a huge battle and says "This is even more epic than that battle in that Lord of the Rings movie" refering to the huge, 30 minute long battle in this film.