I love the handkerchief idea!

In terms of spa ideas, I personally would want the option of going whenever I want-- not necessarily right before or after the wedding. As far as where to get gift certificates for it, do you have an Aveda Institute? I have had my nails done there, facials, massages, all that good stuff... you'd get a lot more bang for your buck! Some people might say that is trashy because it's the school not the straight up salon, but the Institute near me is really nice.