I was watching one of the GCN clips on YouTube the other day and they were talking about some quick bodges you can do to your bike if it all goes horribly wrong whilst out on a ride, that will get you home. I found the puncture repair one good. If you get a puncture and you've no spare tube for whatever reason take it out of the tyre and tie a tight knot in the tube were the puncture is. According to these guys it will seal the offending puncture and will get you back on the road again saving you that long walk home. I suppose you've got nothing to lose if you're marooned in the middle of nowhere without a spare tube .