I'm a firm believer in setting aside a little time every day for yourself. This can be anything from 15 minutes to a couple of hours. I'm luckier than most, I get an hour lunch break at work and most days I can use that time to read rules or magazines or prepare written material for the Blog or my own D&D campaign. But what about those workaholics that don't take a lunch break?
My fist recommendation is TAKE YOUR BREAK. Life's too short to work for free! Even if you end up having a cut down break its worth taking some time away from the desk (or workbench or wherever you work) to think about something other than work. And if you do find yourself with some 'thinking time' why not put it to use constructively. I like to pick on one aspect of my hobby - A plot twist for a campaign; a colour scheme for a model; or an outline for a blog entry - and focus on that. You'd be supervised how productive this method can be and how refreshed you'll feel when you do get back to work.
But what about when you can't sit down and work on something? Such as when your shopping with your 'significant other'. Like most blokes I didn't particularly enjoy Saturday shopping trips, standing outside changing rooms for hours on end. But now I'm a changed man. I take the time to think about small aspects of projects I'm working on. And as a modeler/painter I can turn every shopping trip into a chance to hunt for materials or resources. I usually make a shortlist of items I'm hunting for before we set off and my mission (while the wife shops) is to get at least one of those items.
So, no matter how boring the shopping trip or how short the lunch break, I'm secretly enjoying my hobby and therefore quite content.