The excluding greed part may initially just consist of cutting back a little on our greeds and indulgences. We are trying to change in accordance with Right View and Right Understanding and Right Effort. This means being practical and not harsh or extreme in our efforts to change. I like to formulate it as refraining from doing something and then using restraint and then after some effort the activity or greed is naturally excluded.

“We must protect ourselves from error by excluding greed from our minds”

This third thought, at its most basic level addresses our attitude towards that food and eating in general.
Wanting too much. Wanting only “good” food. Wanting food we like. Wasting food when we have put too much on our plate. To make eating a central part of our daily existence, etc;
Lots of mistakes come from being greedy about food and drink.
This thought also questions our other desires; i.e. wanting approval, sex, relationships, money, status and the myriad other natural inclinations that can tip into greed or overindulgence.
Many mistakes come from being greedy in those areas.
So, greed is a problem; but also our trying to exclude greed from our minds can be problematic.
Some examples are the alcoholic, the over eater, the sexual compulsive, and those other categories where we overly and overtly indulge, often to our detriment. Ask anyone with those issues how easy they are to control, even when they are aware of them.
In Buddhist practice the way we can approach these “greed” aspects of ourselves, is to be willing to look at and try to change the behavior, without being harsh and judgmental to ourselves, by attempting to actively refrain from indulging in them.
When we make these efforts over a period of time we often find some relief. Willingness seems to be the key.
There are other greed’s that can be very tricky because they seem to be good greed’s.
Spiritual greed. Do-gooder/helper greed. Greed for justice and fairness, etc;
We have lots of historical examples of those greed’s getting out of hand.
In the Five Thoughts, we are looking at greed’s that cause personal difficulties. Those greed’s that come between us and a healthier body, a healthier mind, better relations with other people and with our families.
The greed’s that come between us and The Eternal, or our higher sense of purpose.
Like the previous two “thoughts” there is a whole range of meaning and fruitful endeavor to be considered in the activities of our lives.
These “Thought” questions bring up feelings of insurmountability at times, but in the greater context of “Today I undertake to train myself to refrain from…..”, they are logical challenges to be faced and they become part of the woof and warp of daily life; just like getting gas for the car, tending to plumbing problems, brushing my teeth and generally “getting on with it”.
Within all of these daily efforts moments of pure joy can just arise.

Through these mundane small endeavors a sense of sufficiency, adequacy and contentment can appear, and those three results are a more stable base from which to approach daily life rather than seeking mere circumstantial happiness.