Shoot, I keep plugging my etsy site. The mods are totally going to hate me.
Anyway, my son is almost 2, and I made him a "big brother" mei tai ( https://www.etsy.com/listing/101695340/big-brother-mei-tai ) so he can get used to some of the baby stuff. I got this idea when I was babysitting my friend's daughter, who was 2.5 and just about to have a baby brother. Her mom wanted her to spend some time with me and my then-three-month-old son, so she could experience the baby deal. She was completely amazed with my homemade mei tai and how it let me hold him close while still playing blocks with her. I made her an identical one as a "big sister" gift, and now, a couple years later, she still loves it.
We talk about babies needing to be carried because they can't walk, and babies eating from "mama's nipperrrs" as DS says. We have a lot of "new baby" books, and keep getting them from the library. His favorite (which I think is a weird choice) is called _This Baby_, and it's about a little girl wondering what the new baby will be like. It opens with a painting of a girl listening to her mama's pregnant belly--and now DS asks to "listen baby mama tummy" at least once per day. Of course, he does that to DH, too... I think my favorite book (though aimed at a slightly older audience than my son) is the Mr. Rogers one. It deals really well with the feelings of having a new baby in the family.
We're also trying to find opportunities for him to be around young babies in the flesh. It's way more effective, I think, than just videos. Some hospitals or communities offer "big sibling" classes. Although we don't have those around here, it might be worth looking into. When we see a baby at church or out in public, we go over and say hi, and talk about things like how to be gentle with a baby and where it is ok to touch a baby (feet are always a good idea).
I also really love the AlphaMom articles on this: http://alphamom.com/your-life/postpartum/when-the-big-brother-becomes-the-big-challenge/
and http://alphamom.com/pregnancy/gift-ideas-for-the-new-sibling/ .
Oh, and lastly, my brother was born at home, and my dad and I cut the cord together--I actually remember that, even though I was only three. My parents did a lot to really involve me in taking care of him.
Sorry, this are like not at all gift ideas for the most part...