cash is not going to be convenient anymore.
Cash will always remain convenient as long as there is no solid form of fungibility in either digital fiat payments (which won't ever happen) or crypto currencies. Sure, there is XMR and a couple of other coins active in that field, but they aren't being used to conduct day-to-day payments, so it's rather pointless.
Bitcoin's fungibility is going to get a massive boost with Schnorr and Lightning, and I think that's exactly what people are looking for. They don't want a shitcoin that no one cares about doing X, they want a well known crypto as Bitcoin to be multifunctional and do X Y Z because of its global acceptance. It will take some time, but we'll be there eventually.
As long as nothing beats cash's current main utility as a fungible form of money, people will keep using it.