Print out a copy of the tickets (is this possible from the app?), keep a copy of the credit card receipt, and take a screen shot of the tickets (send it to your email -- and, if you're paranoid like I am, send it to another safe email, just in case). While definitely a rare occurrence, the app can eat your tickets, and having the printed and email back up copies can really come in handy in case of emergency. (We recently had a post from someone who had an unused ticket disappear from the app -- so it can happen -- best to be prepared!)