You might want some way to carry and lock luggage to the bike -- a rack or box or something...

I use this but there are lots of others, too: Kawasaki Ninja 400 (18-19) – Ventura (ventura-bike.com)

Here are some pics of mine:

Locking luggage on the back (simple solution)... | Ninja 400 Riders Forum
(8) Diy rear rack? | Ninja 400 Riders Forum

 

What part of Kalifornia? If'n yer in the north, highly recommend an Aerostitch suit. (I like the 2 piece, myself cuz it's more versatile.) It goes on over yer street clothes, 'n is really quick 'n easy to get in and out of, breathes, (Since it's GoreTex) 'n will keep you dry in the rain.
If'n yer in the southern part, you can prolly just get suome Frog Toggs fer the rare rainy day.
Yer prolly gonna wanta good trunk, 'n I like tank bags myself. I like Tour & Ride for all my luggage needs.

 

Southern Cali

 

Ya, two indispensable moto accessories:
Aerostich one piece, R-3, mine is the classic
Givi top case, v46 or your taste.
They can go with you through your moto evolution through steeds and years. They are an investment, and well worth every penny.

yes, speaking from experience:

 

I'll not duplicate the above, but add: Norton Racing Supersport Seat Review

If you don't want to go the luggage route, there's several brands of motorcycle specific backpacks. Some are waterproof.

 

UPDATE: The great thing is I got a job where the company will buy me a motorcycle as a company vehicle. How cool is that?? I need to figure out where to draw the line between protection and all day wearability for riding pants now. My job will require riding 30+ hours a week commuting between their stores stocking their products and placing orders.

 

Excellent dude! Bike's the only way to travel in Kalifornia.
I had a similar gig where I bounced from school to school fix'in stuff. Ain't the best ATGATT, butt I ended up just wear'in blue jeans, 'n an assortment of jackets, cuz like you say, wear-ability is important.
When I had a 60 mi commute, the Aerostitch was great, but seldom wore it in my last gig; only on days w/ torrential downpours. Be'in a slave to fashion, I mostly wore a leather jacket w/ lots of vents I could open 'n close. On hot days, I wore a perforated jacket, 'n light rain days a rain jacket.
You'll prolly want a trunk like Ninjabirds to keep yer helmet 'n riding gear in while at job sites; what I used to do. And a back pack ta keep personal stuff in. I like love Tour & Ride for my MC luggage needs; competitive pricing 'n best customer service in the industry.
Now, what bike are you gonna use, yer Ninja, or get something else?

 

I commute on my bike all year round. As I work in an office I can carry petty well everything I need in my smallish backpack. I also leave a couple of pairs of shoes at work to cut down what I need to carry. For commuting I'd recommend textile gear, which will fit over your work gear. Don't overthink it, and see what works for you.

It's so much better than taking the car or, heaven forbid, public transport.

 

My wife and I each commuted in LA on N400's for over a year. I don't think that there is a better LA traffic, lane splitting, easy handling motorcycle out there than the N400. You will learn to fold the mirrors on the fly or better yet, get N300 mirrors. Any bike that is larger and heavier starts to take away from the traffic ride ability. Congrats on the new job, we just left SoCal after 30 years. I miss the 12 month riding season!

 

You will learn to fold the mirrors on the fly or better yet, get N300 mirrors.

I’m looking forwards to the 12 month riding season! Did you still need to fold your mirrors in when you swapped to the N300’s? Or was it mainly a cosmetic mod?

 

The N300 mirrors look exactly like the N400 mirrors but are a few inches shorter. Still decent rear view viewing but at a little different height and in just a tad from the N400's. Perfect solution for lane splitting. With the original mirrors, you will be right at Prius level and there are 1 billion Prius' in SoCal!! Honda Accords are another car to keep a look out for as far as N400/lane splitting compatibility. I don't think my wife folded in the N300 mirrors at all. I had bar end mirrors. They where never in the way and absolutely perfect for lane splitting but it is harder to view and get used to but I loved them.

My wife's 23 mile each way commute was up to 2 hours until she started taking her bike. It took her :45 minutes to go from Marina del Rey to USC Hospital just east of downtown on the Ninja. She got a big chunk of her life back!!

 

Yeah I visited for a week and the traffic really was ridiculous