Tijuana
If you’re in San Diego, you can easily enter Tijuana, Mexico. David joined me traveling from Los Angeles, USC. There’s a train that takes you to the border. You can then walk over without ever being stopped. Getting back into the USA is more complicated. The customs service will definitely want to see a passport. But walking is pretty easy since there’s not much place to put contraband. So you pass through with minimum waiting. 
The native folks headed to Mexico all seemed to be carrying large bundles of toilet paper. Really! And once you are in Mexico, everyone seems to be bringing back prescription medication. There are big signs and many (hundreds) of pharmacies close-by to the border crossing. 
We just wanted to say we were in Mexico. We wandered around and had tacos. That’s it. No need for drugs, legal or illegal. I would have brought some toilet paper if I had known it was in demand.
You also have to be impressed by the traffic jam back into the USA.
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