CO2 canisters are very useful. Do be careful when inflating your tire since the canister freezes instantly and you could really burn your hand.
I don't have a repair kit with me. I always have two spare tubes with me in my saddle bag.
Another tip:
Try to replace your inner tube at home if you have never done it before. You don't want to do it for the first time when you are in a race.
Thanks for the warning and tip.