Sebastian: We could use bags made of some sort of recycled or biodegradable material, wether its plastic or canvas or something. I liked Stephen's idea to use a bag that can be re-used as a shopping bag, grocery bag, etc.
In the bag could be the water bottle and the IES printing card, along with a guide.
guide could provide not only good tourist info and barcelona facts, but public transportation directions to the most frequented destinations.
A list of "sustainable" stores; whether they are sustainable in their products or in the way they run. grocery stores, clothing, etc.
Info on recycling programs, possibly a cell-phone recycle program.