Recently bought a BB but I wasn't able to update or install packages out of the box. This is what worked for me:
replace original /etc/sources.list with:
deb http://archive.debian.org/debian/ jessie main non-free contrib
deb-src http://archive.debian.org/debian/ jessie main non-free contrib
deb http://archive.debian.org/debian-security/ jessie/updates main non-free contrib
deb-src http://archive.debian.org/debian-security/ jessie/updates main non-free contrib
and run
apt-update
It will give a keyring error. I tried both:
apt-get install debian-archive-keyring
apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com 7638D0442B90D010
but neither worked. Still seems I can apt-get install <package> though.
Next, I ran:
apt-upgrade
and upgraded everything. It gave me a locale error which I fixed with
dpkg-reconfigure locales
(set to en_US.UTF-8)
I have also found a way to get extended LTS until 2025 but I haven't tested it:
https://www.freexian.com/lts/extended/docs/how-to-use-extended-lts/
Hope this helps anyone with a similar question.