[rglullis]

On the Ethereum blockchain, things are a little easier. You can always use a stabletoken like DAI.

On the BTC blockchain, this can be a real problem. The best one can do is to hope that the BTC price doesn't swing more than the equivalent fee amount of a credit card transaction to make it worthwhile.

If you are willing to keep some of your crypto on an exchange (but remember, it is only really your crypto if you have the keys), you can try to automate the swap between BTC<-> stablecoin to reduce the exposure to price swings.