1. sheet of paper (the back of a used envelope would be perfect);
2. a pencil.
Take any exercise. A short jog. Some press-ups. Skipping.
Do some, but stop while you still feel comfortable, even if that is just one press-up or three minutes jogging.
Write down what you did. Decide a modest percentage improvement you will aim for tomorrow. Write it down.
Do it tomorrow.
Continue the process.
You will get fitter.
You will get fit. You just need some paper and a pencil.
More pencil + paper here.