"I do already have my medical card for my home state, but it doesn't mean anything in california."
If you are planning on visiting California, you are welcome to obtain your medical marijuana card. As long as you are at least 18 years of age with a qualifying condition, you can meet with a doctor to see if you're approved for a medical card.
California law does not require patients to be a resident to obtain your medical card. With that said, some dispensaries may ask to see a proof of residency to purchase cannabis, even if you have a medical card.
Depending on your location, you may be in an area that allows recreational cannabis sales. This means, as long as you are 21 years of age with a valid ID (such as a drivers license or passport) you can visit and purchase from a dispensary without a medical card. Some of the major areas that offer recreational cannabis sales include San Franciso, Los Angeles and San Diego.
I hope this information helps! :-)