Fix-a-flat doesn't ruin a tire. Just make sure you tell the tire repair person to get it cleaned out otherwise it will likely gunk up the tire pressure indicator. Fix-a-flat doesn't propel in very cold conditions so you will have to warm it with body heat prior to using. I have a foot pump in the car which won't help much on a quick leak but on a slow leak it might get you to the nearest repair shop.

Personally I despise the mini-tires that come with most vehicles. Sure they are lighter and smaller but not very useful if you have to change the tire when you away from urban sprawl and you are out in the boonines.