The truck is pretty durable in stock form.
Here are a few upgrades that I feel are necessary.
Kill switch - Far more reliable than a failsafe.
Receiver battery - Anything above 4000mAh will do fine.
Air filter - The HPI filter is the standard upgrade, along with an Outerwears pre-filter.
Carb - The stock carbs are junk. A Walbro
668 or
990 is recommended.
Pipe - The stock can is horrible.
Servos - The stock servos are hit or miss. Save yourself some trouble and replace them ASAP. Also, consider running a single steering servo, it's far more reliable and cheaper to maintain.
That's all I can think of, right now. I'm sure others will add on.