The episoded titled "Male Unbonding" had many references to future Seinfeld episodes.
Jerry says "It's not you, it's me" to Joel, just like George said in a future episode. George said he "invented the its not you, it's me routine." That's not true, for Jerry said it first. I'm sure everyone noticed this.
On Jerry's notepad of lies to tell Joel, he says he has to wait for the cable company. This is, of course, ties to "The Cadillac" episode.
Kramer's pizza refers to how he was making his own pizza in the one about Poppie's pizza called "The Pie." Everyone knows about that, right? (from the 100th episode.)
I can't remember the other reference given, for I know there was another one!
Laurie