In old Marshall's office in the end, there is a cutout from a newspaper where the headline is "N.Y.C lawyer captures 'Ness'", a reference to how much Marshall adores the Loch Ness monster.
In Lily's death folder, she says her ATM code is 5459. This spells LILY. This could be a nod to Friends, where Joey's pin is 5639, spelling JOEY.