You'll need:
the group photo from the year before to put on the website
- a skyline of the host city in vector form to be used as a base for other artwork pieces
- an avatar format icon to use on twitter, most likely derived from the above skyline
- attendee materials
- badges for blogs ("I am attending GUADEC" and "I am talking at GUADEC")
- Posters for outreach at e.g. universities
- posters to put up at social events and venues
- banners to go on stage, with sponsor logos on them (which sponsorship logos go on the banners should be detailed in the sponsorship brochure)
- general signs with room names, arrows to give directions, price lists for merchandise, and so on
A large collection of designs was created for GUADEC 2017. It is recommended to reuse them!