Hi James, we buy a lot at the LA county trustee sale and have encountered this problem post eviction. Most of the time when we purchase a vacant property with personal belongings we just throw them away (but it's always junk, nothing valuable). As far as the vehicles, you need to do a lien sale for each one. We have a guy who does them for us, but I know other investors who have done the lien sales themselves and say it's pretty easy.
As far as other valuable personal property (furniture, tools, electronics, etc.) there's a similar process for that. It basically goes to auction, and if no one shows up to bid then title transfers to you. We have had tenants get evicted and try to set us up by leaving valuables then trying to sue us after so it's worth being very cautions when it comes to documenting everything left behind and taking all the right steps along the way.
If you want to send me an PM i'll forward you over the info for the auctioneer we use