What would you do if you don't have any space around you to keep save your stuff; e.g.: your cell phone while you're exercising.

Put them on the ground (Considering that somebody may stumble with them).

Put them away from you (Considering that you may receive a call from someone very important and you will not be able to hear the cell phone when it rings).

Don't carry your cell phone, or other things with you to the place you exercise in.