I got multiple times to 48+ hours, the thing that always kill the efforts to reach 72 hours is headache, no amount of brot and salt saves me. Hunger is not an issue after the first day it generally disappears.
In any case, recently, I swapped to just having a healthier lifestyle, I walk at least one hour 5 days out of 7, do weights twice a weak (mostly body weight exercises at home). Never felt better in my life, I find other approaches silly. If you're not disciplined to do X for your own health and well being fix the discipline, don't change the approach.
Also, it helps that I do this while working. I can do lots of stuff from my phone, including reviewing PRS, mails or pushing small fixes as I walk through the park.
I still plan for an occasional fast once a month of 36 hours, but haven't committed to it yet.