I don't mean the whole Prison-Woodbury "war" should have happened in Season 2, I mean they should of slightly hinted to it's upcoming introduction. What I mean by that is that the shootout in "Triggerfinger" should of been between Rick and Woodbury, but of course he doesn't know it. Martinez (Jose Cantillo) should of shown driving away in Woodbury's modified Ford Excursion similiar to Nate in the white pickup truck. The person that Rick captures should have said something along the lines of "We got a barricaded town, 20-30 armed guys".
In addition to that, Rick could have come across a dead group of survivors with all their belongings taken.
Somewhat of a foreshadowing.