Being a teaching assistant can give you a taste of the other side. If you always thought you could be a better teacher than those profs you had, then this is your opportunity to prove it. You may discover that you really enjoy teaching or that it is not for you.
Once you start to work on your thesis project, then what you get done depends on the time you want to spend. You can even allow yourself to be distracted and work on some other things that may be of interest. Perhaps you want to learn more about how our computer system works. You can volunteer to help our system administrator keep the place running and learn valuable skills at the same time. Sometimes, a number of students will get together and build some project that they think is fun, but it is not their thesis. There are many opportunities to learn things and few barriers to doing so within the available resources.
If you are entrepreneurial, then you can use the opportunity at graduate school to work on some idea, and benefit from all the fancy equipment and facilities available that you could not afford yourself. Of course, you better keep in mind the university's policy on intellectual property, which is quite fair to start with.
If you think you would be happy with any job that pays a reasonable salary, then stop reading now, and surf some other sites.
If you worry about brain rot and need to be constantly stimulated, then do not settle for that job offer you have now. Graduate school will keep your brain fed and give you many more opportunities in the future (see previous item). Of course, there are always exceptions. For example, a new company is forming and you will be right in there living or dying with their new product.
In fact, many of our Ph.D. graduates get job offers (usually not in Canada) that pay more than their supervisors. Even some of our M.A.Sc. graduates get paid more than some of our newer faculty members. If you wanted to be a prof, do you still?