For overseas travel as MurrayM had pointed out, I normally have the travel correspondence received via email in my gmail account

I always have a scanned copy of my passport and etickets , hotel bookings on google drive that I delete after my travels.

I carry a photocopy of partner's and my passport scaled down in my wallet.  Beats the hassle of taking out the passports when filling forms on flights as I cant

remember all the details like PP numbers, dates of issue , expiry date etc.  

When flying SQ I always have a print out of the boarding pass when I complete online checking.  Seems a waste at times as 

they re-issue another boarding card.