No tampons for me... I'm a Diva Cup girl and will never go back to pads or tampons. The cup
http://www.divacup.com/ (I don't work for them!) is something I rave about. (There are a few other brands, but I haven't tried them). Instead of absorbing the blood, it collects it. You collapse it and insert it over your cervix internally and it collects blood in a cup. Depending on how heavily you are bleeding, you need to change it every 3-12 hours. Personally, at the start of my period I only have to change it every six hours, to give you an idea of why I'm mentioning it here. The "every 3 hours" mark doesn't happen for me until more than halfway into the first day, or the second day, and doesn't last very long. If you know you might be having your period the day of your race, you put it in, just in case. Even if you don't expect your period for a few days, you can still put it in. You'll never have an "accident" again. I happen to be regular, like clockwork, but if you're not, that's an even better reason to wear one on race day.
There is a steep learning curve, so you can expect some leakage for the first up to 3 months that you are learning. If you fail to insert it properly, you might have leakage. After you figure things out, you'll wonder why you ever settled for barbaric things like tampons!!! If you are planning to use it during a race, you should practice for at least three months prior. I don't have to use one during a race unless I'm expecting my period.
The bonus for triathletes is that you can go swimming with it in... it's like a plug. When I'm using it, I sometimes forget I'm having my period. The only thing that reminds me to change it is when I start feeling moist "down there" which means it's nearly full. You can cycle with it in, without even noticing it is there. The bonus for the environment and for your pocketbook is that you never have to buy and throw away a pad or tampon again! You just keep washing and re-using it. I've had mine for two years and it's actually working better than when I first bought it. The other cool thing is when you go on vacation and you're expecting your period, you don't have to pack a wad of tampons/pads but only need to pack the tiny cup.
In fact, I can't see a downside except the learning curve. If you are learning, just use a panty liner for backup. The other problem with it is that you need to wash it, rather than the disposable culture of the tampon. Seeing blood doesn't bother me, but I would guess it would bother others. I buy the Diva Wash by the same company to make washing easier.
Highly recommended for triathletes and women who care about the environment.