It is an inevitable fact of life that your Wedding day will be like every other where you'll have to wonder about "what not to wear" in terms of undergarments (of course, when you're draped in a fabulous satin faced-taffeta dress, the annoyance level escalates just a little).
I spend on average 5-10 times a night at Weddings pulling and tugging the Bride's dress up so (guys cover your ears) the "girls" don't make an appearance. But honestly, there's just got to be a better way. My advice if this is of concern, and especially if you are "well endowed", is to avoid strapless if you can.
Now, I love strapless as much as the next person. I understand that it gives a beautiful neck line and something about it makes you feel "gorgeous", but on your Wedding day the last thing you want to feel is self-conscious because you're so concerned that the dress of your dreams keeps slipping. One option if you have to go strapless, is to have your seamstress create a halter strap to add to your dress during the reception. You can still walk down the aisle and have pictures in your strapless gown and then at the reception you won't be afraid to dance. If the halter is just not going to cut it for you, please invest in very good undergarments- WACOAL has an amazing seamless line as do many other designers. Be careful though ladies, I forewarn you, the stuff is addictive!