Learn to embrace the "one thing." Don't try and do it all at once... you don't have to. Multi-tasking was for your old life, the one where you had way too much to do with not enough resources and no chance of succeeding.
Leave that life behind in your too-small office cubicle, and change your perspective. No more cramming all the weeks' chores into a couple of days. Try doing one thing a day instead, and let the lack of urgency help you learn to relax. (But if your idea of freedom is running around the county doing errands and visiting friends, shopping and sightseeing, by all means go for it!)
For the first month of retirement, I was content to carry on with my usual tasks each day, but also gave myself time to read, to answer e-mail, to browse through the stacks at the library, and I finally got my shopping done at Ikea. If the sun was out, I worked in the yard. If it was raining, I'd inventory the wine cellar or do some sewing, or maybe just catch up with my journal and write for my blog.
Being content with one thing worked great for me... give it a try.