Storing a removed drive shaft is best handled with a sock. Place the sock over the U-joint and it will hold the caps in place and prevent the grease from getting smeared anywhere.
Caught in a jam with only a standard wrench to try and turn a metric bolt or nut? Spare change from your pocket, like a penny or dime, can be used to slide between the wrench and bolt, taking up the slack and allowing you to turn the fastener.