...real world range is affected (grapevine, AC, etc)
I haven't gone that route with Model 3 but I've frequently done between Visalia and Orange County with no problem.
Your range is dependent on mostly your driving style.
Mine is quite conservative so I let the Autopilot does the work for me most of the time and I observe the speed limit (65 to 70 MPH depending where on CA-99 and I-5.
So before I start my trip, I would charge up to an additional 50 miles which has done the job.
My trip distance is around 220 miles so I don't leave until the battery gauge says 270 (220+50).
Grapevine/Tejon pass elevation of 4,144 feet seems not to affect my range at all because the regen would regain most back.
I haven't encountered headwind but that would surely eat up energy: I want to observe my speed limit of 70 MPH but if headwind is 20 MPH, that's an equivalent energy consumption speed for 90 MPH!
Modesto to LAX is about 310 miles so no I don't feel comfortable doing that without charging in between.
I in a hurry and driving alone, I might not want to stop in between for a 310 mile trip in a gasoline car but that is not healthy for my bladder.
If I have passengers with me, stopping to charge in between a 310-mile trip is painless because I have to holler to my passengers that 1/2 hour break time is over and it's time to get back on the road.
Back to driving alone, I would Supercharge at either Tejon Ranch or Santa Clarita for a quick break and some more miles to drive around LAX. A 15-minute charge would be more than enough for that purpose.
Good luck!