Write as much info about each job as you can. Make sure there are no time gaps. I would only completely omit a job if it was 'without papers' - i.e., if the government didn't know about it, you got no pay slips, and didn't declare the income for taxes. Even then, I would include the job if it lasted for a while.
Then if there is some info you don't remember and can't find out, just include a note explaining that.
There were also several time periods within the 5 years that I was jobless due to going to school and travelling. I will explain that but would that effect me badly in any way?
The part where you said 'completely omit a job if it was without papers'. This particular job I had lasted maybe 2 months, only twice a week, and I did not send it the tax forms that I should have. After I quit the job, the boss at the place was asking me for it but I was in another country at the time for a several months and ended up completely forgetting about it by the time I came back to Canada. And as much as I regret this I jumped around from job to job a LOT during this 5 years. Would that make me look bad?