Tires.
I did skid plates, full set, as #2, but if I were to do it all over again, it would be suspension #2 and skids #3. Note that I say suspension and not lift (mine is just 1.3.1).
The stock tires cannot handle any half-serious terrain let alone the desert. I know a guy who got stuck in a place where no Subaru would have been--or 4R on any AT tires. And a journalist on stock tires got stuck in a couple inches of snow with the Subarus driving by a few years ago. Plus punctures, etc.
You don't want to drive over rocks big enough to need aftermarket skids on stock tires. And the small, fist-sized rocks over which we all drive in the desert are nasty.