Things that fit the purpose, work, still just as relevant or are very nostalgic keep an interest.
Digital receipts may be nice, but there's an old saying along the lines that to really foul things up just use a computer. It shouldn't be that way, a well managed database with sure fire back ups isn't a problem ... the problems fall more often to, poor backups, an inability to quickly search the database either being a poorly designed database or one with a very poor limited interface ... at other times it's just PEBKAC.
But paper receipts are also easy to loose if one has entrusted a clown to pick up supplies, as well as theft if the receipt is more than just a general invoice.
Smart phones though ... ymmv ... after having an android ... or two fubar unexpectedly, suddenly with little apparent hope of retrieving any data ... email dockets stored in some secure stable email server [never the fubar prone device] are decidedly a better option.