Reset thumbnail cache on Android Gallery

Go to the directory:
/data/data/com.androids.providers.media/databases/
and delete the file external.db. Don't touch internal.db.
To be safe you can just rename it so you can restore the file later.

Reboot and the thumbnails are all deleted. Android will recreate them after a little while, depending on how many images you have.

This worked for me on Galaxy S2 with custom ROM.

Recover missing SIM toolkit icon on Android if it has disappeared

My SIM toolkit suddenly disappeared and after try a number of options, this is what worked for me on an SGII, Android 4.2.2

Enable SIM lock - (make sure you know the default SIM lock code before you do this, check with your operator)
Reboot phone.

That's it.
Apparently on some phones it can reappear by enabling flight mode and disabling it but that didn't work for me.

Hope it helps. Let me know if you found any other ways of getting it back.