A chore that you could be doing that will increase your fitness is yard work. Yard work is something that always needs doing and can always provide you a workout. It's a great way to kill two birds with one stone. You can get some needed activity by getting out and working on your outside lawn space weekly. Time will fly by, as both your yard and your body begin to look great.
In order to strengthen your core and develop a great midsection, do not be afraid to perform full range sit-ups. Compared to crunches, sit-ups make your abs work harder and longer as a result of the increase in the range of motion. Just be sure to avoid performing sit-ups with your feet anchored to the floor, as this can cause injury to your lower back.