Started with a backpack, moved to a military style helmet bag which I used for many years and then got luck and picked up a Briteline package when the FBO was getting rid of their flight shop. When just flying for me, I use the helmet bag. Flying for business, the Briteline.

As others hinted at decide if you need it to do multiple functions (fly, school, office, weekend), how much space do you need (more pockets is not necessarily better) and what's the budget. A helmet bag is $30-ish online and the thrift store is a great place for other small bags. Go with what works for you.