What to do in a gap year before going for a postgraduate study?

I have just graduated with a MMATH degree and I want to apply for a phD in Mathematics but it is a bit late now so I am thinking of applying around December for the next academic year. But I don't know how I should spend my gap year. I have tried looking for Data Analyst jobs but most of them are permanent so I don't want to apply for those jobs. Any ideas what I should do in my gap year?Thank you.