How should you prep for hardware failure?
Communication is key. Only you know your teams tolerance to downtime. I've worked with teams that people get fired after 10 minutes and others where downtime is a welcomed excuse to take the afternoon off.
Do yourself a favor and ask the hard questions to you vendors.
Check Amazon, NewEgg & local suppliers.
A stick of RAM may be easier to source than a power supply, but the power supply may take the whole system down.
The best thing you can do it talk to you vendors and prepare ahead of time. Trying to deal with it in the moment only adds time and stress.