Mine stays clipped to the back cover of my US passport since I need both to travel. In the same place I also keep an Excel spreadsheet listing my travel dates in and out of Canada including my destination, purpose, and whether or not I was traveling with my citizen partner. Might want to set up a system to document your comings and goings as well. You'll need this info to renew PR card and/or apply for citizenship.
But if one is not leaving Canada, no need to carry the PR card. (Better have a trip list, and remind yourself to go get the PR card if you are leaving Canada.)
A previous poster said to carry the PR card when travelling to different provinces, because some Canadian cities are near the USA. I don't understand that advice; you don`t need the PR card for travel within Canada, and the city`s proximity to the USA doesn't matter. Only if you actually leave Canada do you need your PR card (perhaps you need it too enter the other country, and certainly need it to re-enter Canada). So, normally you can put the PR card away for safe keeping.
The Excel trip history will come in handy for renewing the PR card in 5 years, but I don`t see the need to carry it with you on trips until you have passed the 3-year mark. Before that point, you have two years to go, and that is plenty of time to meet your PR quota -- even if you have not spent a day in Canada until that point.
After that point a border officer MIGHT ask you to prove that you will be able to qualify for PR renewal by the date of your deadline. Showing a trip history that guides the officer through your passport will provide the assurance necessary -- that and a bottle of scotch.