Shopping wise One by K has very nice quality shirts/sweatshirts.
https://www.wearesxm.com/shopping/one-by-k/Calmos Cafe itself has a very nice shop attached to the restaurant.
Marigot market has a lot of stuff/junk but there is a lady who sells hand painted tiles/magnets of local beaches or island scenes which are a great gift to take home.
https://www.st-martin.org/us/learn-more/culture-and-heritage/marigot-market/ I personally wouldn't bother going to Philipsburg unless you wanted to buy jewelry or some expensive booze, especially with limited time.