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.