Are you already into significant off-roading, or are you just getting started?
Well, either way the answer should be the same: the best first mod is no mod. Instead of throwing money around in random directions to try to solve a problem that you haven't encountered yet, spend some time with your new Jeep and try to figure out where the weaknesses are, based on what you're doing with it. THEN start looking at modifications that will solve those problems.
Stock Jeeps are already extremely capable machines. You may find that you don't even NEED modifications for what you are planning to do with it.
That said, maybe a set of grab handles or a cart to hold your doors during the warmer months would be a good place to start.