Could be using gift cards purchased with bitcoin via nostr:npub1m7r9aayrqjtt2q0whkyrwlys75s5d828c5uewvqwyfd2kxefkfjqgeny2w, that is my go to. 

Or using Strike app to convert to fiat when necessary or perhaps via credit card then pay CC off with bitcoin. 

There are a number of ways. Depends on your situation.