Turning 50 is a milestone birthday year, a time when it seems almost inevitable we think about the past and contemplate the future.

Investment manager Brian Gustafson used the occasion of his 50th to write a short book just for his four children to read. "Smile: 50 years in the making" is a charming combination of memoir, family values and personal legacy. ("Smile" is family shorthand for: service, mindset, integrity, laughter and effort.)

The section that focused on creating a late-in-life work roadmap intrigued me. The "10 of 10" list details jobs he would like to do within a 10-year period (actually, he lists 11, but who's counting?) that have nothing to do with his current position.

"They are occupations that I'd like to hold for a short period of time, approximately one year each, to experience a variety of lifestyles that would be deeply nostalgic, romantic and intrinsically rewarding … for me personally," he wrote.

The jobs: Minneapolis Parks employee, letter carrier, grocery carry-out, Peace Corps recruiter, Bruce Springsteen and the E Street Band roadie, farmer, Linden Hills Co-op employee, golf course caddy, consultant, musician and Minnesota Department of Transportation maintenance crew.

Something of an unexpected list, with a few realistic jobs and others closer to fantasy. He learned a lot about himself thinking through what he might do next (which might change with age).

"Will I consider myself to have failed if I do not complete my 10 in 10?" he wrote. "Not at all. Instead, I'll have benefitted from a vision that led me down a compelling road, even if not all the way to the road's end."

Thought exercises like 10 in 10 are worthwhile at any time, but they can be particularly valuable during major life transitions. We're living longer, and we're living healthier lives, on average. The gift of longevity offers an unprecedented opportunity to imagine what we might do next and to ask: "How do I leave the world a better place for myself, my family and my community?"

Reinvention coach John Tarnoff recommended a similar exercise. When thinking about a mid-career change, he encouraged people to set aside half an hour every day to jot down thoughts, hopes and options. The act of writing helps organize your thoughts. Journaling is also popular.

Question is, what is your list of 10 (or however many) ideal jobs?

Chris Farrell is senior economics contributor, "Marketplace"; and a commentator for Minnesota Public Radio.