I agree with all of the above. When making a booking online it's best to:
1) Take a screen shot of the confirmation page, which will include the reference number and itinerary, along with any ticket restrictions.
2) Save the email somewhere safe. If you don't receive an email, it's usually because your email provider has rejected it as spam without your permission. It happens all the time, and I frequently have to look at logs to prove this was the case.
3) If you receive neither of the two, or you lose them, please give us (or whoever you bought the tickets from) a call. For example, we're always happy to answer the phone and chase up any missing reference numbers. We always keep them on file here.
4) If something goes wrong during the collection, ring us (or whoever you're using). Most of the time it's a problem with the machines, but we'll talk you through the process and make sure you don't lose out financially.
5) If everything goes wrong, and it's not your fault, and you can't get hold of anyone, buy some new tickets there and then and we'll make sure you son't lose out financially. But that wouldn't cover you just forgetting the booking reference. But even then, you could still get a refund on the original tickets, and we would often waive the refund fee (depending on circumstances).