What to do with dead times during your PhD?
The best thing to do in the summer after your "third" year of PhD is to take stock of where you are and where you want to be. Then you want to create a plan to get there - basically, write yourself a realistic roadmap, working back from what a successful job search looks like. 

In Economics, you will be focused on the job market in year 5. You will want to be prepared to convince committees that you are a good hire - that you are prepared to hit the ground running and get tenure at their institution. Look at the CV of the hires from this round for your ideal institutions and compare your CV. Do you need another paper? A grant? A major award? Make a list. 

Then create your calendar. Put on important deadlines. Plan when you want to submit other things and what the turnaround is likely to be (it will be long). 

Keep in mind that the fifth year is basically a wash. You don't achieve anything of note. You may finish an R&amp;R, but other than that, refining your job market paper and your presentation plus applying to and interviewing for jobs takes all your time. If you are not clear on what that year will look like, read some of the excellent job market guides from AEA or Econ bloggers. Also consider the book "The Professor is In" or Vitae columns. 

Given this, I would probably argue for thinking hard about grants and what proposals you might want to have ready to send during year 5. This involves some real generative, creative work. It means thinking about what you want your research agenda to look like as an Assistant Professor. Having this sort of thing in the pipeline will be impressive to hiring committees.

Once you have done this, you should also consider doing things that make you happy. See some family and friends and get some exercise. Or do something vaguely work related but actually pleasant like creating your website or signing up for some summer institute/workshop. This summer is the last time you will have to really kick back (presuming you are worrying about moving after you graduate)!