summer internships aligned with search

For those who had a summer internship or similar period sometime before searching full-time: what was the most relevant and valuable short-term work experience you had? Did you round out your professional experience in some way? Return to your field of expertise? Intern at a company in your target industry or geography? 

For current MBAs interested in search: how are you planning on spending your summer?

For investors or those who have seen a few different search funds: is there a common denominator that you wish more searchers had up front, that could be gained in a few months?

I was in the military prior to business school, and am pursuing investment banking this summer. A traditional MBA offers a lot of flexibility - I am curious how one might best leverage that flexibility if search is the goal (either immediately following graduation or mid-career).