The BEST thing to wear under the dress is one of
these!
They sell them in stores - go get measured to make sure you get the right size so you can still breathe. I wore mine for my wedding and as a bridesmaid and it sucks you in, smooths you out, AND makes you stand up straight! Since it has a layer of padding, it makes everything look toned and not just squished like the spanx style ones
Spanx bottoms are an option but I bought according tot he size chart and I couldn't even put them on. So go a size up or get a shaper that is not so constricting. I think control-top pantyhose are sufficient and they even have the shorts kind now.
Treat yourself to a mani/pedi and get your hair and makeup done so you don't feel self conscious. They will be taking so many pictures you want the professional look. I'm not a spa person, in fact I haven't had a mani/pedi since I was a bridesmaid, but I would do it again for an event like that.
You can get the double stick tape at bridal shops but recently I've seen it at Target and Kohls in the underwear depts! We used it to hold up our strapless dresses for 12 hours of wedding festivities