I bought this bag because I am doing boxing and I needed a larger gym bag. It is very light weight when it's empty - probably less than a pound. It is made of Polyester. The color I bought was Black and Grey but you could also get it in Sky Blue and Electric Blue.
Inside the bag is very large and it even has a built-in shoe bag. You actually access the shoe bag from a zippered pocket placed on the outside width of the bag. There is also a zippered pocket that could fit small item like your combination lock for the lockers or MP3 player. The outside of the bag has 2 pockets - one large zippered pocket the length of the bag and another pocket on the width of one side. There is also n air vent for the shoe bag. There are 2 kinds of straps for the bag - a smaller strap to carry is in your hands and a larger strap to carry it over the shoulder.
This bag can hold my boxing gear, gym shoes, towel, toiletries, etc. and still has room to spare - you can really pack it in!