I keep emailed copies as PDFs and usually have these on my lap top or a USB drive as I travel.
When starting a journey from home, I print my pass onto thin card. For my work, I have purchased A4 sheets that are devided into three Landscape sections with micro perforations. Once you've sorted and saved the margins and page settings, you can print the 'active' part onto a piece of card that is just about the same size as the old ATB card - minus the mag stripe! This means I can leave behind the useless advertising that the (I presume) the car hire company has paid the LCC for. If it's a short trip, I can print out and back cards at the same time.
Check in and Gate Agents raise an appreciative eyebrow at the card but it always works and you can stick the bag tags on the back.