There's a tradition that the bride should wear something old, something new, something borrowed and something blue for good luck. The "something new" symbolizes looking forward to a bright future, according to the editors of "Martha Stuart Weddings" in a CNN.com article titled "11 Wedding Superstitions and Traditions Explained." Show your sister that you approve of her marriage and her future with her fiance by giving her something new to wear on her wedding day -- perhaps diamond earrings or a new bracelet.

Give your sister something that will remind her of your life together. Find an old picture of the two of you, and have it restored and framed. Or give her that old jacket of yours that she was always borrowing -- without permission -- from your closet. If your sister plans to have children, dig out her old teddy bear, have it repaired if necessary and then tie a ribbon around it and tell her to save it for your niece or nephew. You can also simply give her the gift of your company -- ask her if you can take her to breakfast on her wedding day, and then take that opportunity to tell her how much you love her and wish her the best in her marriage.

No, you shouldn't get her a toaster, but there may be an act of service you can perform for her that she will treasure always. If she loves cleanliness and order, consider hiring someone to clean her house so that everything is sparkling when she returns from her honeymoon. If she likes flowers, sneak over to her house and plant a pot of gorgeous annuals on her porch, so that when she leaves her house on her wedding day, she is greeted with a beautiful surprise. Alternatively, hire and pay for the best hairdresser in town to do her hair for the wedding.

Give her a gift that keeps on giving. If she always wanted a puppy, for example, but your parents wouldn't allow it, give her a certificate for a new puppy that she can use when she's ready -- perhaps when she returns from the honeymoon or buys her first house. Consider indulging her favorite vice by giving her a gift card to her favorite coffee shop or subscribing her to a snack-of-the-month club. Think of your sister's personality -- after all, you know her better than almost anyone -- and use that information to generate ideas.