Inner tubes? I've been told (I don't have them) that if you have a puncture with an inner tube, it goes pop and that's it you need to replace it. But I bet you could pack about 4-5 inner tubes into the car if needs be. And carry a spare anyway, to make changing one to get you out of a situation, easier (you'd sort the punctured tyre at a better spot or end-of-day). I've heard (but not sure) that with inner tubes, its less likely you'll suffer a puncture too.