This Is just what comes in the comes in the core set though.
In the core set you get 5 different upgrade cards to play with
Out of the 5 cards, 3 are rebel only. As in they can only fit on the Xwing as the Xwing has upgrade slots for EPT (pilot skills) Astromechs, and Torpedos. The TIE fighters (and not all of them) only have access to the pilot skills and there are only 2 of those.
Lets take a quick look at the rebel ones first
2 droids and some Proton torpedos. Both the droids are defensive in nature as opposed to the torpedos
The 2 usable by the Empire here are Determination and Markmanship. One defensive, one offensive.
This is just to give you an idea what comes in the core set. Each ship you buy also comes with more and different upgrades too.
Watch out for articles in the future where I go into what upgrades work well in combos with pilots for the missions in the core set.