A transaction is essentially just a signed cryptographic message broadcast to the network, just imagine that instead of broadcasting it, you keep iterating on it, you pass funds around, keep signing these messages, etc. There are measures to make sure you don't broadcast an old/outdated transaction to the network.

It's not meant for buying coffee, for those you would use layer 2 or centralized entities like Paypal, etc. The blockchain contains every single transaction ever made forever, people in 100 years from now don't need to be aware of every coffee transaction, that just wouldn't be efficient.