When I get an emailed coupon from a store that I frequent (Michael's, JoAnn, Hobby Lobby, Fresh & Easy), I take a quick screenshot of the coupon on my phone by holding down the power button and the Home button at the same time. The screen will flash and the image is immediately saved in the photo album.
It looks like this:
TO ADD AN ALBUM click on the photo album app > Edit (top right) > Add (top left) > Name Your Album (Coupons)
And all the coupons for the week (or month) will be in one place for easy access (and stress-free checkouts).