How does he go from picking her up to being in bed together?

The 80s were great

People weren't as sexually repressed in 1980 as they are these days.

Ha! That's what every heterosexual male would like to figure out...

Because it’s Tom Atkins.

Also, it’s customary to pay for ass, gas or cash....or something.

It was just a little more than a decade after the summer of love. People, especially on the west coast where this movie is set, were more relaxed about casual sex. There was birth control but no AIDS (not generally, anyway). It was not a big deal.

You must be young.

Their conversation was hinting that she had been looking for a good lay after hitchhiking for some time.

I'd gotten him to have a round in the back of the truck before we made it to his place

Not unusual, I've hooked up with people I knew even less than that, for some of us it's like a handshake