It takes a while for the water to get warm when I shower. In its place, I can...
a) stare at myself in the mirror
b) wander around the house
c) watch TV
d) do some push-ups
D is fun and good for you! Using the sink, I place my hands so that they create a perpendicular right angle in my elbows, my body is in a plank position at approximately 45 degrees since my feet are about 3.5 feet away from the sink. Imagine it for a second (if you don't have as much bathroom space, adjust your plank angle, you'll still get a good work-out). 12 reps.... twice... and water is ready and my arms are just sore enough to have worked out a bit.
Not sure if it works.. but it sure feels good to do something productive in a mere 3 minutes.