if you are using bitcoin then maybe today 1 apple is 0.0008 btc , but tomorrow with 0.0008 btc you can buy 2 apples, but if no one used bitcoin for shopping then there won't be any shop that will adopting bitcoin anymore
so what will be you choice?
As much as possible, fiat will be the one that will primarily used on any kinds and type of spendings whether for online and offline transactions. Well in the first place, that is an obvious thing to do even prior to the existency of bitcoin.
So with bitcoin now as a bonus to our usual financial life, it must be saved and will just be spend if it's really needs or in a such a case that can be called "no choice" or just want to try how bitcoin works in online transaction.