You need to backup wallet.dat file. There are your private keys, that with u can access urs bitcoins.
So you either export plain private keys from wallets or backup whole wallet.dat file and move them on new computer to use ur bitcoin from there.
That is a great plan except I wouldn't do either or of them but rather I would do both of them every single time you move your wallet because if your dat file gets corrupted you no longer have access to the coins! Get down both as a precaution but for future private keys are more important than wallet.dat if you had to and could only obtain one.
I agree, more backups the better but remember also, that you need to keep all that backups secure also.
Minor extra job, but needed to maintain appriopriate security level
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