@ae_rollinson, excellent suggestions!  Keeping a copy of the paperwork you mentioned has saved me numerous times.  During my first PCS, I was charged for my graduation leave.  Luckily I kept a copy of my leave form, so I was able to get it taken care of relatively quickly.  You never know when some of that paperwork will come in handy.  Your suggestion about keeping documents from your landlord and utility companies is also a great idea.  The utilities office from Germany just messaged me after I cleared them 11 months ago.  Fortunately for me I was able to resolve it quickly.  Otherwise, as you said, it could be hard to deal with problems without having all of the paperwork and contact information once you leave.