The personal items left in the car really leave you with a limited number of possible scenarios.
A) Went swimming/surfing/boarding and ended up in a rip current or other water related mishap.
B) Left the car to hike or swim/surf and was intercepted by unknown individual(s). Possibly removed from the LKP by boat or vehicle. Potential for the unknown individual(s) to be couch surfer related.
C) The car and contents are a diversion by party or parties unknown to encourage LE and SAR to spend time and energy on option A allowing time and distance with the hope that in the end LE and SAR abandon the search in the assumption Tiffany was swept out to sea.
The Park Rangers would sweep the park at closing and discover the car and declare a SAR or missing person event after their hasty search came up empty.
I don't know what to think about that seeing the the car wasn't in the lot the day she went missing.
from http://www.huffingtonpost.com/2013/08/21/tiffany-daniels-missing_n_3791494.html"A neighbor that lives in a condominium across the street [from the parking lot] said that car was definitely not there two days ago," Huntsinger said.