1. Bring the I-485 approval notice or relevant document to the USCIS local office in your area to get a stamp on your passport and then, you can travel.
Also;
2. File Form I-90 for replacement of the lost green card. See http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=b3f7ab0a43b5d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=db029c7755cb9010VgnVCM10000045f3d6a1RCRD