Our daughter was 2 1/2 to the day when our son was born. We had him give her a one of the stuffed animals that you get to name a star with and she gave him one as well. Her grandparents also got her a big sister book and a friend of ours got them big sister/little brother shirts. When I found out I was pregnant, we had also gotten her a "I am going to be a big sister" shirt that she insisted on wearing every week. We also made it a point to talk about the baby and the fact that she was going to be a big sister and that mommy was going to need her help once he arrived. I had a scheduled c-section, so she had a special trip to her grandparents where she stayed while I was in the hospital. She came each day to visit and was brought home the day I came home. We have her help get diapers, wipes, keep him occupied while changing, feeding, etc. I also made sure no matter what, that each day I spend at least 15 minutes of alone time with each of them. He is now 13 months old and they adore each other. And she still helps with him getting diapers, trying to feed him, etc.
Congratulations and good luck!