Hi there!
Well I don't tend to do much either... but my definite would be concealer and eyeliner! lol
Nice and simple!
Of course, it helps to apply your concealer with a concealer brush because it helps with getting it just right. I find that fingers are just too imprecise with this!
Eyeliner... well it depends on what kind of liner your using I suppose. I think pencil is probably the easiest to handle out of all of them, but I personally love the fluidlines that mac makes
In that case though, you'd need an eyeliner brush to go with it.
Depending on your skin... and how used to it you are, you may or may not want to try foundation? It was a big step for me at first... covering my face with just... STUFF hehe so you might want to try tinted moisturiser or something along those lines first if you aren't comfortable with foundation!
I think it really depends on what you're looking for, and your skin type and so on- and of course, what you'd be comfortable with using since I'm assuming you don't usually wear well... anything.... though most girls do tend to wear at least mascara and eyeliner nowadays, so I don't know if my presumption is incorrect
From there, your list just keeps going up and up and up! Oh! And don't forget the blush... and probably something to fill in your brows with!