apt

# Stretch
 
deb http://security.debian.org/ stretch/updates main
# Line commented out by installer because it failed to verify:
deb-src http://security.debian.org/ stretch/updates main
 
deb http://mirror.yandex.ru/debian stretch main
deb-src http://mirror.yandex.ru/debian stretch main
 
deb http://mirror.yandex.ru/debian stretch-updates main
deb-src http://mirror.yandex.ru/debian stretch-updates main
 
deb http://mirror.yandex.ru/debian/ stretch-proposed-updates main non-free contrib
deb-src http://mirror.yandex.ru/debian/ stretch-proposed-updates main non-free contrib
 
# Backports
#deb http://mirror.yandex.ru/debian stretch-backports main contrib non-free
#deb-src http://mirror.yandex.ru/debian stretch-backports main contrib non-free

Virtualbox
echo 'deb http://download.virtualbox.org/virtualbox/debian stretch contrib' > /etc/apt/sources.list.d/virtualbox.list
wget https://www.virtualbox.org/dow[..]oracle_vbox_2016.asc -O- | apt-key add -