Here is a list of goodies that you can buy to support the event. The are pre-paid and will be handed to you at your arrival at the Drupal Devs Days.

It's a pre-order: we need to order a minimum number of items per goodies. You can see the progression of the orders.
If the minimum number is not reached before the limit date (mainly 15-03-2015), the goodie won't be made and you will be paid back.
You need to have bought a ticket to the event to be able to order goodies.

Spoiler alert: A free totebag will also be supplied to handle these ;)