Here are some popular things that expats do in Spain to make extra cash
Although totally illegal, this goes on a lot in Spain. Being an unofficial taxi for other expats is dangerous as using your car for hire is against your insurance and you need to have a licence. However, many people ignor this and offer 'lifts' to the airport, under cutting the expensive Spanish taxis. Be careful if you do this. Never let money change hands in the street. If a taxi driver sees this at the airport, you will have major trouble on your hands. I personally have seen expats attacked by taxi drivers.
Meet and greet
On your urbanisation, there may be lots of apartments that are let out to holiday makers. Owners often look for someone to manage the apartments for them. This might involve meeting the holiday makers and handing over keys, preparing a welcome pack with essential groceries or just being on hand if they need anything. This type of job is perfect for someone who is semi-retired and just wants ocassional little jobs.
If you like to keep active and have transport, local free newspapers take on people delivering to shops and other drop-off points. They also take on people delivering leaflets.