Stay on a schedule. Set your alarm, get up and do the morning routine stuff, get breakfast/lunch/dinner around the same times and go to bed around the same times each night. Set a limit on how long you dawdle around the house. Plan on one errand/outing a day. Could be grocery run, go for a bike/hike/gym, do the laundry or whatever. But get a routine down and don't go off the rails with the late nights, hours on the computer doing fuckall, or forgetting when you last showered. It is too easy to just fall into this type of slothfulness when you're suddenly free from all major commitments.
Do you want to work? If so, start getting your resume spiffed up, contact colleagues and other companies you've worked with in the past, and start looking around for gigs. Definitely consider doing contract work since you don't want a full time schedule. Put the word out that you are interested in short term stuff and since you're technically FIREd, you don't have to take anything that doesn't sound fun to you.
You also could technically go look outside your field of expertise since you're not dependent on the payscale. If you have interests or skills that you never tapped before, check that stuff out. You literally could start over in a brand new career if that sounds like an intriguing challenge.
And again, no money necessary? Volunteer work is a super avenue to explore. Check out charities in your area that you have an interest in. You could do basic stuff, or you could also offer your skills in your former career if they have a need/use for them. In any case, most places will let you volunteer as little or as much as you'd like and set your own schedule. I personally work at a wildlife rehab, a therapeutic horse-riding facility (for children), and eventually hope to work on Habitat For Humanity stuff.
You could also concentrate on yourself. Get healthy by learning how to cook better foods, exercise, take up some new hobbies, go back to school (not for a degree unless that sounds like a fun challenge), clean and organize your living space and streamline/curate your collections or stuff... there's tons of things to do. ;)
