I assume you'll be going HWY 80 Donner Pass? I'm not 100% sure, but I think CHP requires you to at least carry chains even if you're a 4WD, so it might be a good idea to have some on hand in case they check. I know WA State almost never requires chains on 4WD (it's not the norm), but they can and will require them if conditions are bad enough. Cali DOT should have a website with this info, so maybe do a search for that just to verify. I know it can get nasty up there on Donner, aside from just being a shitty road!

As far as what to get, I'd probably just go to Wal-Mart or something and get some cable chains just for the rear tires so you have them if they stop you and ask. It's doubtful you'd have to actually use them, but it would suck to get all the way up there and be turned around because you don't have them with you!