That’s - Taco Tuesday. I think on Tuesday tacos are half price at Rubios and probably other places as well.
And this is a tangent but for conservation concerns, Rubio’s is pretty responsible -
http://www.rubios.com/socialresponsibility/sustainableseafood/
Another thing to do in SD that people might have already mentioned - wandering tide pools. This could be in La Jolla just south of the Children’s Pool (a cove with a lot of seals) area, on Pt Loma just down from the Cabrillo Lighthouse (a historic monument) and a variety of other places. Download a free tide chart app for your smart phone to figure out when to do what at the beach. There are usually a lot of colorful (green mostly) anemones, small crabs, small fish, and miscellaneous other things to try to find.