I keep two thorn resistant tubes in my pack, I've got a tire iron and a hand-pump on my bike, for emergencies, and quick releases on my wheels. I learned I'd need these things when riding down a hill once, I got to the bottom and both tires were leaking. =/
Unfortunatly, slime sucks on a road bike, specially when you get some real speed. I keep a couple tubes, standard, couple Co2's and a patch kit. just swapped the kit for a new one cause I didnt want the same thing to happen.