When apt-get update shows the following error with only debian repositories:

W: There is no public key available for the following key IDs:

The simple fix is to install the debian-archive-keyring package and repeat the update process

apt-get install debian-archive-keyring
apt-get update

For google chrome repository and error:

W: There is no public key available for the following key IDs:
1397BC53640DB551

The fix is to:

wget -q -O - https://dl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

For other NO_PUBKEY errors, make a note of the ID, then use

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys KEY

In case of dpkg dependency errors of a package that isn't configured yet, trigger configuration manually.
Example error:

 dpkg: dependency problems prevent processing triggers for libglib2.0-0:i386:
 libglib2.0-0:i386 depends on libc6 (>= 2.28); however:
  Package libc6:i386 is not configured yet.

sudo dpkg --configure -a