Wow, that is a fun adventure.  Obviously bring a smart-phone with a wallet app installed and wait for the actual transaction to appear in that wallet.  I use coin.space for a portable wallet.  The wallet itself should cover an appropriate number of confirmations so you don't have to deal with it.  Copy and paste the TX ID somewhere in a document in the phone and email it to another person, just to confirm the date and time.  Biggest thing is that even a few confirmations can take a long time.  Find an outside restaurant because you could be there a few minutes or even an hour or more.  Have fun and don't hand that money over until the transaction is in your wallet history.