Toyosu Market is three visits on three different clocks: the before-dawn tuna auction, the market breakfast, and Senkyaku Banrai. Which one you want sets your alarm.
Koenji's vintage shops sit mostly south of the station and many stay shut until 13:00, one until 15:00. The north side opens earlier and sells different stock.
Shimokitazawa's secondhand shops open late in the day, and the district is not automatically cheaper than Koenji or Harajuku. What to check before you buy.