When I asked about this, the hospital told me that I'd have to have the blood collected by the red cross and then do some other paperwork to get my blood on standby at the hospital if I needed it. They also told me that normally, additional blood isn't needed.
Well, I wasn't normal!!! And , I have rare blood.
I found out later that I was on the table for about 12 hours because they couldn't get the bleeding stopped. They told me that they used something like 20 units of platelets!!?
I'd recommend banking some of your own. If you don't need it, someone else will.