If you're comfortable billing for lunch, you're probably not charging enough. I'd tend to agree though that you should be charging for debugging, but I've had some things where I couldn't in clear conscience charge for. Things like troubleshooting an issue with my tooling that went beyond just 'sharpening my ax for the job'. Especially if I'm using a job to try out some new tooling, rather than using something tried and true.

That said I understand getting to daily or weekly rates can really let your rates take off, and you don't have to worry about what time you're on the clock in the same way.