As said above definitely. Also, if you have enough room in your breeches, you may want to consider a second pair of underpants - that helps act as a bit of a buffer and also helps keep the pad in position.
Also, Make sure the size tampon your using can hold what your putting out. I know I can soak a regular quickly on my heavier days. If I ride l'll go for a super or a super plus. I love the regular/super/super plus combo packs they sell now! Posted via Mobile Device
Agreed on doubling up on protection. Because I flow heavily on the first couple of days of mine, I always wear a pad along with my cup (I use a Diva cup instead of tampons because tampons make me cramp horribly).
Tampon (if you can use them), pad and double up on the underwear or wear a pair of white stockings under the white breeches. Go to the bathroom whenever you can to check on how things are going down there and catch any leakage as early as possible. Ah the joys of being a woman! I can only remind myself that at least I can't land on two extremely sensitive organs if my horse chucks in a buck.