I've worked a lot of random jobs; bike mechanic, bus driver, warehouseman, theatre technician, systems support specialist II, web developer, plus more. I've only ever prepared specialized resumes in the past. When writing up my CV, should I include everything I've ever done, or should I leave out things like being the district public skating supervisor/first aider when I was 15, and working in the Photo-electronics department at Superstore when I was 18?
The answer depends in large part on where you are in your career. As a hiring manager, if I look at the resume of an experienced engineer I'm generally not interested in roles held before graduation that are unrelated to the field or position.
For someone still starting their career, additional jobs can be interesting, but if I'm looking at a college graduate, I'm likely to gloss over anything in the pre-college era.
Continuity of employment is important after graduating college, but I won't question gaps that might appear during high school and college. Your focus should be on your education at that phase of your life so gaps are easily understood.
If you did something noteworthy in one of those early jobs, or they highlight application of skills important to the position, then maybe include them. But the further in your past they are, the less relevant they become.
If I were interviewing a candidate for a web developer position, say, the fact that the candidate waited tables or taught skiing or whatever as a teenager is noise that I ignore and might as well not be on the resume. I would much prefer to see a resume tailored towards the job.
That said, I've in the past included one weird job on my resume. (Monkey boy; I chased down escaped monkeys when I was a teenager.) That sort of thing can be a nice way to have fun / start a conversation / be memorable / etc. But a whole long list of them seems excessive.
When I worked in theatre the Props Master (my boss) showed me his CV, it was comprehensive. It detailed ever position he had ever held as well as every production he had ever worked on.
Maybe this helps for "Fine Arts" in that it shows you have had experience doing X so you have an understanding of that part in the real world.
I was encouraged to make CV the same way when taking my portfolio class in University.
Likely as you only had these "bit parts" to work with.
When writing up my CV, should I include everything I've ever done
Are you continuing in the "Fine Arts" area? If so ignore me, I have no exposure to that space. Otherwise I do not think having a "comprehensive CV" will ever give you value for the time you spend on it. I take it you currently have a direction in life? Write a reasonably "comprehensive" CV for that direction (which will serve as the bases for the CVs/Resumes sent out). Anything that does not show something that can benefit you in that direction remove or reduce to a line.
A lot of companies like to see a contiguous list of jobs on a CV, and questions are often asked about any gaps, so I'd suggest putting it all in, albeit briefly.
If there is something relevant to your current application in one of those jobs, make a point of calling it out. Otherwise I'd suggest a single-line description of the role and/or why you took it and save space for the jobs they'll be interested in.