Choose the driver before the first drink
If the group will drink, choose one sober driver for the whole return or use a ride. Do not make the decision after the last stop, and do not plan for anyone who has been drinking to drive. TxDOT's road-safety guidance gives the same plain advice: impairment begins with the first drink; designate a sober driver or call a ride.
If a car may stay behind, ask the venue before leaving it there. Do not assume a public lot is an overnight option: the South Padre Island traffic code prohibits overnight parking in public parking areas where posted signs say so. Save the lodging address in the phone that will arrange the ride, and pick a meeting point before the group splits up.
For a music night, Lobo Del Mar and LongBoard give a West Palm starting point; for dinner, use bar and grills. The getting around guide is the place to compare island transportation options. If someone needs a different way home, make that choice early and let them take it.