What part of the country do you live in? A good set of tires is your best friend when it comes to offroading. The BFG all terrain is a great all purpose tire. Even though I have 4x4, I do most of my offroading in 2WD. Having an automatic locker (Detroit or Yukon Grizzly) gives me some great performance offroad without 4x4, but if most of your driving is street, you may not want that. You may want to consider a front bull bar with a winch. Not having 4x4 may lead you to get stuck more than you like and some good recovery gear will go a long way.
MOST IMPORTANTLY-Make sure your runner is in top working order. It sucks to get out in the middle of no where and have your engine die for some stupid reason or another. Make sure your suspension and breaks are fully functional as well.