Fitness Kickboxing: Don't give me any slack.
To add a little spice and variety to your bag routine change your spacing from the heavy bag. Normally, you stand with the bag hanging in front of you in a neutral position as you punch and kick. The bag will swing away from you and then eventually swing back to you like a pendulum.
Now try something new. Position yourself so that you are standing in that space the bag once was -- with it pushed away from you. This creates a situation where the bag is constantly loaded to come at you. Now the pacing of your blows must increase to keep it from crashing into you. With gravity now favoring the bag over you, each strike you throw will also seem to land on a bag that weighs twice as much as normal.
This type of drill in the beginning is best done in short bursts with just boxing techniques. As your skill, timing, and endurance increases you can also add kicks into the combination equation. NOTE: In some cases if the bag is mounted fairly close to a wall, you may need to stand "behind" the bag to do this drill. This is the situation in our Dojo, for example.