Encrypted and secure docker containers

What you are asking about is called obfuscation. It has nothing to do with Docker and is a very language-specific problem; for data you can always do whatever mangling you want, but while you can hope to discourage the attacker it will never be secure. Even state-of-the-art encryption schemes can't help since the program (which you provide) has to contain the key.

C is usually hard enough to reverse engineer, for Python you can try pyobfuscate and similar.

For data, I found this question (keywords: encrypting files game).

The root user on the host machine (where the docker daemon runs) has full access to all the processes running on the host. That means the person who controls the host machine can always get access to the RAM of the application as well as the file system. That makes it impossible to hide a key for decrypting the file system or protecting RAM from debugging.

Using obfuscation on a standard Linux box, you can make it harder to read the file system and RAM, but you can't make it impossible or the container cannot run.

If you can control the hardware running the operating system, then you might want to look at the Trusted Platform Module which starts system verification as soon as the system boots. You could then theoretically do things before the root user has access to the system to hide keys and strongly encrypt file systems. Even then, given physical access to the machine, a determined attacker can always get the decrypted data.