The age old question, should you carry spares racing?
You can, and often it saves a long walk back to transition if you do flat, but there are some other alternatives. It is possible to pre-inject puncture repair fluid into the tube, and if - heaven forbid - you puncture in a race, and your sealant of choice works, you'll hear a short pssscht, followed by the tire magically healing itself. Usually you'll only lose a couple of PSI, not even enough to worry about stopping for.
There are a couple of products on the market that purport to do this:
Vittoria Pitstop, which is a pressurised latex foam in a can, which cost me 3rd at the 2008 worlds (got 9th instead.) Don't bother with it - it is inferior in a lot of ways, and is also not recommended by a number of people I know!
I think the main issue is that the foam is too light inside the tube to actually stem the airflow through a cut, and so the tyre ends up deflating anyway. I've attempted to fix 3 other punctures under non race conditions, with every one failing.
I should add that most of the Vittoria tyres are actually a good product, it is just this particular product that is not worth purchasing.
Get some Doc Blue or Stans liquid sealants from your LBS.
Insert the goo BEFORE you race
Follow directions on the bottle (Unscrew your valve core, insert recommended dose of fluid, rescrew valve core, pump up and ride for 5km)
I've fixed 3 tiny sized glass flats on a very expensive front tubular glued on a race wheel this way. The tube is overglued (better rolling resistance, and that is a whole nuther article) so not that keen on having to take it off and either put a new tubbie on or get the old one fixed.
Sure you still have the dilemma, should I carry spares, but now you have some added race insurance!