Switching from jessie to jessie-backports with support for installing stretch/sid packages. (/etc/apt/)

preferences

Package: *
Pin: release n=jessie-backports
Pin-Priority: 800

Package: *
Pin: release n=jessie-updates
Pin-Priority: 700

Package: *
Pin: release n=jessie
Pin-Priority: 600

Package: *
Pin: release n=stretch
Pin-Priority: 300

Package: *
Pin: release n=sid
Pin-Priority: 200

Package: *
Pin: release o=Debian
Pin-Priority: -10

sources.list

deb http://ftp.pl.debian.org/debian/ jessie main contrib non-free
deb-src http://ftp.pl.debian.org/debian/ jessie main contrib non-free

deb http://security.debian.org/ jessie/updates main contrib non-free
deb-src http://security.debian.org/ jessie/updates main contrib non-free

# jessie-updates, previously known as 'volatile'
deb http://ftp.pl.debian.org/debian/ jessie-updates main contrib non-free
deb-src http://ftp.pl.debian.org/debian/ jessie-updates main contrib non-free

# jessie-backports, previously on backports.debian.org
deb http://ftp.pl.debian.org/debian/ jessie-backports main contrib non-free
deb-src http://ftp.pl.debian.org/debian/ jessie-backports main contrib non-free


# stretch
deb http://ftp.pl.debian.org/debian/ stretch main contrib non-free
deb-src http://ftp.pl.debian.org/debian/ stretch main contrib non-free

# sid
deb http://ftp.pl.debian.org/debian/ sid main contrib non-free
deb-src http://ftp.pl.debian.org/debian/ sid main contrib non-free

sudo apt-get update
sudo apt-get dist-upgrade

Now you'll get some more recent stuff like Wireshark 2 (1.x is so buggy...) or LibreOffice 5.
If you want to install some packages from stretch/sid use -t RELEASE option, e.g.:

sudo apt-get install -t stretch html-xml-utils
sudo apt-get install -t sid jq

Some packages from sid may require to upgrade a lot of already installed packages, but fortunately it's not always the case. There are some useful newer versions available in sid, e.g.:

• GnuPG 2.1