Thanks for all your answers, it's definitely helping!
I guess I should have been a bit more specific.
I don't ride when it rains (Yes I live in Portland, OR so these days I dont ride that much ;-)
and thats why I though about saving money by not buying waterproof panniers.
I am very new to all the commuting gear but I have heard about heelstriking with the panniers. Is that common ??
I am looking at a Topeak Explorer rack but havent made a move yet.
What I need to carry is a change of clothes (jeans, shirt, underwear, shoes), my lunch (usually 2-3 tupperwares), wallet & notepad, some misc small items, possibly my laptop and another change of clothes if I go run on my lunchbreak