Usually, if I miss a workout, it's because I'm overwhelmed by my to-do list.
Luckily, things like chores can actually burn a few calories. It's like killing two birds with one stone.
That's definitely the case for cleaning out your car. I found that out recently, after driving through the car wash. I took some time to vacuum the seats and floor of my car. I threw out a few things. I was lucky - my car wasn't too full of junk. It took me about ten minutes. But in that ten minutes, I burned 40 calories! (That's according to my Bodybugg, which I wear every day on my arm.)
40 calories isn't bad at all, especially when you compare that to actual exercise. Take for example... running. If I run a 10-minute mile, I burn about 100 calories. So it's not too bad, if you just need to get some stuff done!
I'm not advocating that, instead of working out, you clean up your car instead. I'm just offering up the good news that - when you do have to vacuum it out, you're going to burn some calories.
And if you don't go through the car wash like I did and you actually wash it yourself... you're bound to burn even more calories!