A home-made strap for my pants. For a few RM you can purchase a meter of velcro. Cut an appropriate length and you have a pants strap. It will protect your pants from getting tangled up on the chain ring, and getting grease on your pants, especially on your right leg.
A leg band from a bike shop may cost you anywhere from RM20 a piece. Of course, they are nicer and come with reflective strips.