Maximizing my Muji A6 notebook

In the past, the frequency of changing my EDC (Every Day Carry) notebook is about once every month or every 1.5 month.

It will be about 12 notebooks for a year. It will cost me about USD40 (SGD$50.00) a year if I use Field Notes Original 3-pack.

For 2015, I am saving up for some big project coming my way;
I decided to cut down on spending $$$ on notebooks (and fountain pens).
1 method is to maximise the use of my notebook - to use all the available spaces if possible.