In my case packages held back were those related to linux-headers and kernel. I came to this by trying to solve an issue with having a red exclamation mark in the notification area and not being able to update packages.
To solve it, I did not have to use neither dist-upgrade nor manual apt-get install xxx.
What I did and has helped has been simple and clean:
sudo apt-get update
sudo apt-get autoremove
sudo apt-get autoclean
sudo apt-get upgrade
I had to manually confirm Grub update and its configuration.
Then I just worked with the computer for a while and then standard update dialogue has appeared again finally including "Ubuntu base" section with kernel and related. The update was performed without any trouble and I do not see any held back packages any more.
Also, it is very important to keep in mind that those *buntu updates including kernel updates are sensitive to hibernation - I've got this problem several times and I always get it resolved by restarting the machine and performing the steps above.
So maybe this would be just enough?!
(situation being described in here is related to my Xubuntu 15.10 in the end of december 2015)