The "get your development environment set up" session used to include MediaWiki setup with Vagrant. Our conference wifi couldn't handle 25 simultaneous attempts to download a 300-megabyte file, and most of the workarounds we tried were insufficient, so we've decided to instead be more thorough about getting Git set up. If you want to set up Vagrant and MediaWiki, and are having issues, and the instructions on mediawiki.org are not helping, you should contact User:MarkTraceur, who is at the event. Ori Livneh, who is also at the hackathon, can also help you.
Topic on Talk:Amsterdam Hackathon 2013
Removing MediaWiki from "getting started" session
Can we do a mirror on the local network or something? (For next time...)
I agree - a local mirror, or something like it, would be better for next time.
Hand out CDs! :D
Yes, these are all good suggestions. We should look into adding programmatic support for pulling boxes from a local mirror, if it isn't in Vagrant already. CDs / USB sticks would be nice too. I filed bug 49057 and will follow up with something. Sorry to have not been more responsive on this thread until now.
USB sticks are way easier... especially for those of us without CD-ROM drives. ;)