Day 1: DB inclines x 3, BB rows or chins x 3, skullcrushers x 2, EZ curls x 2
Day 2: Squats x 5
Day 3 and sometimes 4 too: Rest
...repeat.
Now and then I'll toss in something completely different, just do delt raises or leg extension/curl supersets or something, but 15 minutes of intense work and I'm out of there. I do spend a minute or two beforehand bouncing up and down and waving my arms about though - it's important to warm up.