I've got a Nikon D700 which is my working camera, and I was in the same situation. It's a beast to take anywhere casual. I picked up a Nikon N80 super cheap and it's my favorite for walking around. Has all the control of your F100 and none of the weight. Put a 50 1.8 AF-D or 24 2.8 AF-D and some Tri-X and you've got yourself a great combo.

I also just picked up an FE and a 24 2.8 AI. It's a nice combo too, but a lot heavier than the N80 although smaller. I'm using it for slides.