My monthly grocery budget is pretty large, but the first part of "no spend" is to stick to that budget! For that reason, don't do a "no spend" around Thanksgiving or Christmas, or any month you know you will be feeding extra people a lot of food. Every time I go to the store, I add up my receipts and write it in my weekly planner so I keep track. One week, I may hit a discount store like Aldi for my necessities, just to make sure I stay under budget.
The next part is to use what you've got. I am an avid reader and read every night before bed. This means I go through a book on my Kindle every 3-4 days. Ten books a month can add up! So, for no spend, I go back and re-read old books - sometimes even *gasp* printed books! I also dig into my pantry and freezer to use up food, and into my linen closet for all the hoarded shampoo I forgot about.
Lastly, give yourself a break. You can't foresee every occurrence. One of my kids broke my laptop adaptor and made off with the cord - resulting in an extra $100 purchase. Life happens.
My goals is for 4 "No Spend Months" in 2018, so we will see if I can do that!