We've had a number of hackathons at Sainsbury's over the years, which enables us to create innovate solutions quickly to known business problems. Hackathons have usually took the shape of working in teams across 2 days in the office, although locations have also included Microsoft Innovation Lab, Google and a poultry farm!
Building over 2 days forces the team to be lean and really focus on the value you're delivering to the business and also the end users. This has stood me in good stead to work leanly and put into practise many of the techniques and frameworks within the UX/Product lean playbook.
Working across 2 days means you have to retain a laser focus on value to constantly focus on, and re-evaluate value, within rapid iterations to constantly test and learn. This has been applied to all products that I've worked on.