This requirement is what confuses a lot of people. I believe that they could've written it more clearly on the checklist. Some couples don't have insurances, some don't need to support each other financially, but they have lots of other proofs. Obviously living together can't be proven if you're not applying inland. On the other hand, a rental lease agreement and then having the same address on a driver's license is the easiest evidence out of all. Outland applicants will get those right away after moving to Canada. It should be more for common-law than married couples. It says "one document from 3 of the following sets of options", then in some categories it says "minimum 1 document", and in some it doesn't - what? Weird.
We are preparing our application and we have so many proofs of our relationship, but they mostly apply to the last category that talks about being recognized by others. As well as messages and visits, because we are not living together. We also have financial support information. Also, lots of more evidence that doesn't fall into any of those categories that much. We just can't seem to get any proof for a 3rd category. We can get life insurance right now but I think it's better not to force it just for the application - they will know it was done last minute etc, instead it's better to provide an explanation. You can provide an explanation for everything, things like: No one attending the wedding, family not knowing about the relationship, no visits to see each other, etc, so you can also explain why there was no financial support or no insurance. I believe they don't care as much about the 3 categories as long as you provide enough evidence of your relationship, as well as they want you to not go beyond the limit with photos and conversations. They just want to guide you. It's understandable that you don't have insurance or you might not have it yet before going to Canada, as well as you can't get other proofs that are all connected to just living together. Correct me if I'm wrong but that's how I understand it.