It's a minor detail, but everyone always says to get a bunch of death certificates.
You might not need to.
I looked into it for my state, and they're about $15 each, and you can order them any time.
The only reason I can see to order extra is to avoid the delay in waiting for them to arrive so you can use them. If you're working through things slowly or in priority order, you'll be able to see the situation coming.
Many (most?) places will return the original after you send it.
Many places don't need the original, just a scanned copy.
We ordered 10 for my Mom when she passed; I think we used three (net) and I still have the other seven in a folder somewhere.
If you're organized and know his situation, you can probably count up how many you will need. Maybe order a few extra, but not 10 extra.