Well California goes both ways, either screwing you or getting screwed, but imagine 10-17 rds in your G-17, I would get a few 50 RD drums too if it was me.
During the window of 3/27 to 4/5 when people were allowed to get them I sent messages to a few friends living in the occupied territory and recommended getting as many 30-rounders (classic size for AR's and AK's) as they could lay their hands on but also recommended getting Magpul D60's, in my opinion the most reliable drum-style magazine available. Anything larger and the weight of all that ammo starts to be a hindrance. There are some larger drums available but their reliability has never been as great as Magpul.