Well, you can name another person as POD — payable on death — on your I-bond purchase. See this article. Then that person would need a copy of the death certificate and proof of identity to have the bond transferred into his or her own name.
If you don’t name a POD, then the bond goes into your estate, to be distributed according to your will.
And if you die without a will, some agent of the court will determine who gets your money! So at the very least, make a will!