You could be transacting your coffee with any crypto that Starbucks supports, and which is compatible with the lightning network. Litecoin will work for this example.

So Starbucks ask you to pay via Litecoin, which is fine by you even though you don't have a Litecoin balance. Atomic swaps over lightning network funded by some bitcoin you own, converted to Litecoin, is how you'll pay for your coffee.