I'm just wondering about those random people who turn up as crime victims on your Law & Order/CSI type shows or otherwise always have small parts. I'm not talking about the famous guest stars, just your average actor.

Like Bree Turner:

http://www.imdb.com/name/nm0877430/

55 appearances, but almost all small roles: A singer during the opening credits of My Best Friends Wedding; random appearances on dramas like Cold Case and Ghost Whisperer; "Dancer #1" type roles; random girl with a couple of lines in a movie.

Do people like this make a good living? What do they do in between roles?

Bus tables.

that's about right

OP: it depends.

If it's a one- or two-day guest star, they make a minimum of $782/day, but most actors have a day quote that's more than that.

Guest star/top-of-show, like when somebody is a central character, is around $4500 for 1/2 hour shows and $7000 for 1 hour shows. AFTRA and SAG rates are slightly different. Some actors have the clout to demand top-of-show even if they're only working a couple of days.

Then you've got people that are celebs, etc. They top out around $25K max for a guest star.

It's very difficult to make a living doing guest star roles in TV. The only people making a lot of money on TV are series regulars.

What do they do between roles? Try to get other roles in TV, film, and commercials. Sometimes print. Sometimes other jobs. If I were a young hot actress I'd be a table-service waitress, that's the most ludicrous gig imaginable.