During my rest weeks I focussed on stretching and cardio. I did two days of yoga workouts, 1 day of Pilates and 3 days of cardio such as kickboxing and step aerobics. I avoided lifting any moderate to heavy weights to give my forearms a rest.
I agree with Hazlady - yoga and cardio as the go-to workouts. Depending on how I am feeling, I sometimes fit in hiit training in addition to steady state. I usually fit in a metabolic workout using light weights once during the week.
I try to get to some enjoyable outdoor pursuits during my 'fun week' - biking, running, hiking, swimming, tennis, cross-country skiing or just long walks. It is nice to mix it up and have some fun and fresh air!