Bitcoin Core 0.13 BIP32 support BitcoinCore 0.13 now supports BIP32 wallets. Documentation states, that if I create a new wallet and encrypt it, it will be an hd wallet. Then I can make a one-time backup of the master secret key.

Imagine that I do all the steps listed above. I start generating addresses and accepting payments. I do not make any backups. 

How can I restore my wallet at any time in future (with all keys generated after the initial backup?)?
Correction: I had thought that Bitcoin Core implements BIP44, which it does not. Thus, what I previously wrote about the gap-limit was wrong.

To restore your wallet-backup you place the wallet.dat into the Bitcoin Core data directory as Pieter described.

When Bitcoin Core is started, it will load the wallet.dat. The wallet.dat includes the information up to what blockchain height it was used last. So, Bitcoin Core will now from what blockchain height to search for additional transactions. 

Hereby, Bitcoin Core will generate a key pool of, by default 100, unused addresses that it also checks for. Whenever it discovers a transaction corresponding to any of its addresses, it will generate more addresses from the deterministic chain to fill the key pool back up.

To recover addresses beyond the key pool, you can just request new addresses in Bitcoin Core until you have found all your funds. This type of initial backup doesn't allow you to recover meta-data such as notes about the transactions' origins or recipients as they are only stored in the wallet.dat and cannot be recovered from the preceding backup.