We always take some Euro's, not lots but 100 to 200, if we don't use them all, we bring them home and take the the next yr. This winter bought gas on the french side and the exchange was 1.2 to 1 so used Euro's. Same in the Marigot market when we bought some souvenirs. Bought some pictures on the french side, they started at 1.2 exchange, but after realizig I would use a cc instead if the exchange stayed at 1.2, they changed and came down a bit, so I paid in US.

I think the original poster said they were mostly staying on the french side, so not sure what they are bringing

J&B