There is a fitness plan developed by the Royal Canadian Air Force, called the 5BX Plan, which contains a set of just five exercises to be performed in 11 minutes. It's at least 40 years old, but still very relevant today.
I had a PDF version of this in my old (as in the late nineties) PC, and subsequently lost it. Google searches didn't really help me because I mistakenly thought that a) it was called the 5B plan and b) it was the RCMP who developed this.
I contacted the RCMP, not really expecting a reply, and was pleasantly surprised to receive the PDF from a very helpful gentleman.
My earlier experience with the plan was not very successful, as I presumptuously skipped the earlier charts and started in the middle; I stopped after three or four days after my body threatened to go on an indefinite strike. This time I am starting at the bottom, and going by the book. It's been five days now, and my body is holding up pretty well so far (touch wood).