Not sure if I should carry coins for public transport in Cuba or if card payments are common. Advice?
When it comes to public transport in Cuba, it's cash all the way. It's not a place where you can rely on digital payments or credit cards. The traditional shared taxis and private cars all operate on a cash-for-service basis. Negotiate your fare upfront and make sure you have small bills of Cuban pesos (CUP) to pay. This is the most reliable and common way to handle all your transport needs.
It's a very simple answer: you need cash. There's no card or payment app system for public transport in Cuba. The public transport network, from shared taxis to motorbikes, is all based on cash transactions. So, before you get on a vehicle, make sure you have enough Cuban pesos (CUP) on you. You can get cash from a local bank ATM, but don't count on being able to use a card for a ride.
Don't even think about using a card for public transport in Cuba. The system is entirely cash-based. I took a few shared taxis and buses from Havana to other cities, and every single driver expected cash payment. No one has a card reader or even a mobile payment system set up for this. My advice is to have a good supply of Cuban pesos (CUP) on you, as it's the only way to get around reliably.
You should absolutely carry cash for public transport in Cuba. The buses and shared taxis, even the ones for tourists, are a strictly cash-based system. You will not find any card machines or digital payment options. Both the Cuban peso (CUP) and the US dollar (USD) are widely accepted, but it’s best to use local currency. You can get CUP from an ATM at a bank like Banco de Crédito y Comercio. You'll need cash for everything from Viazul buses to shared taxis.