At the moment, you need to create a channel with our lightning node to pay. Our node is:
0361eea926879867367c310c6b2bbf27ef4510c879dfd428126edadef825648fe9@159.89.7.135:9735
The simplest wallet to use is Eclair. It can be found in Google Play store. Eclair also have a desktop version. Eclair requires to lock a minimum of 0.001 Bitcoin in a channel (other wallets don’t). What was not spent gets back to you once your close the channel, so the locking is only temporarily.
More elaborate instructions for to buy using Eclair and c-lightning is here. A third popular implementation that was already used to make a purchase in the shop is lnd.