What is the first item (or make it top three items) you would replace on a Trek Fuel EX 5?

I’m looking at getting this bike, but are aware that most factory bikes are not perfect, and that most times you would like to make some amendments to them. So I’m wondering what you would change first, maybe even from day one?

Here’s a link to the specs of the Fuel EX 5:

http://www.trekbikes.com/au/en/bikes/mountain/si...

Thanks!!