Don't buy pot there, you'll get ripped off and or have to buy it from some grungy gangster wannabe.

Im guessing if you enter from Northern California you won't have much of a problem at all, but if you enter near the south the border patrol gets a lot of Mexicans trying to transport brick weed and they'll be better trained to spot it.

Just don't be stupid, wear nice clothes and address the officers as 'sir'. Look like a tourist.