Spit. That's what we use.
Specifically hers. However, in terms of anal, I've found that once things get going it tends to lubricate itself.
I've found that spit works pretty well in getting things going before actual sex.
I don't really buy lube ever. Seems kinda bizarre to me and I've never had an issue where lube was required (because I put effort into that thing called foreplay... word up to that).
I found a tube of KY in my back seat here a while ago. No idea where it came from. I think it was a practical joke by some work folks.
Yeah. I choose spit.