Aruba uses the Aruban florin (AWG), pegged at 1.79 AWG = 1 USD. US dollars are universally accepted. If you have leftover florins:
Florins don't expire. If you return, you'll avoid exchange fees.
Local markets (San Nicolas, Oranjestad), duty-free, artisan shops.
Colorful banknotes (2019 series: 10, 25, 50, 100, 200 AWG) feature Aruban wildlife/landmarks—distinctive souvenirs.
Service staff appreciate florins (avoids their exchange hassle).
Note: Coins (5, 10, 25, 50 cents, 1, 5 florin) are harder to exchange abroad—spend or donate them.