December 30 will be Saturday so restaurants and supermarkets will be open like any other day.
I recommend you to visit the Malaga city centre lights and martkets, you can check our post about Christmas lights in Malaga
. The train might be a good means of transport for this.
The Christmas markets in Fuengirola are at Plaza de la Constitucion.
New Year's Eve in Fuengirola is celebrated at Plaza de España.
For New Year's Eve restaurants or accommodation I would recommend to book in advance.
Enjoy your visit to Fuengirola!