These two lines — gan qi shi（甘其食 — to savour their own food）, mei qi fu（美其服 — to wear their own clothes well） — are easy to misread.
Read them as "eat fine food, wear fine clothes" and you have walked off somewhere else. That is luxury, not what chapter 80 of the Daodejing means. Gan（甘 — to savour, to find it sweet） is finding it good to eat; mei（美 — comely, fit to be seen） is looking decent. Both words describe a person's relation to his own days, not the price of things. (Our own renderings, not a quoted translation.)
Start with gan（甘 — to savour, to find it sweet）.
The same bowl of noodles is delicious when you are hungry; set it in front of you right after three banquet meals and it is a burden. Gan（甘 — to savour, to find it sweet） is not in the bowl. It is in the person.
That explains why the "best meal" so many people cannot forget is usually no famous dish. It is the bowl of leftover rice in the pot when you came home from school. It is the wontons at the stall downstairs when you worked past midnight. It is the taste of home you ate after years away. By any standard of "is it good," those things may not rank. But at that moment they fit that person exactly.
So gan qi shi（甘其食 — to savour their own food） is not "eat as well as you can." It is "you can get it down, it tastes good, and after it you feel settled." That a person can be satisfied with an ordinary meal is not a lack of ambition. It is his days having made peace with him.
Now mei（美 — comely, fit to be seen）.
This is the word most easily used as a stand-in for "expensive." But in classical Chinese, mei（美 — comely, fit to be seen） here means decent, presentable, fit to be seen — it is about measure, not price.
A shirt washed pale, with no fraying at the collar, is decent to wear out. A very expensive garment in the wrong size, for the wrong occasion, is not. So decency has little to do with how much was spent, and a great deal to do with whether the person took the thing seriously.
And the subject of mei qi fu（美其服 — to wear their own clothes well） is oneself. It is not "others see it as beautiful," it is "I find it presentable." The two often differ: clothes worn for others to look at are often uncomfortable to the one wearing them, and clothes that are comfortable may never be noticed by anyone else.
So the difference between decency and luxury is this: decency is toward the occasion and toward yourself (I took today seriously); luxury is toward others (I want you to see).
One serves the days; the other serves the gaze. The first gets cheaper the more you use it. The second gets emptier.
So what does "making peace with your own days" mean?
It means you no longer measure your life with someone else's life as the ruler.
If another household makes a ceremony of three meals a day and one bowl of noodles is enough at yours, that is not you living badly — that is you living your life. If someone else wears a garment for a season and you wear one for five years, that is not shabbiness — that is you being comfortable.
Here is the hard part: a person accepts "I ought to live better" very easily, and accepts "what I have now is good enough" very hard. The first sounds like ambition; the second sounds like giving up.
But the two are not actually in conflict. A person can keep improving his days and, at the same time, be satisfied with what he already has. Gan qi shi, mei qi fu（甘其食，美其服 — to savour their own food, to wear their own clothes well） speaks to that second half — the half almost nobody says out loud.
The words gan qi shi, mei qi fu（甘其食，美其服 — to savour their own food, to wear their own clothes well） — we keep them as a saying.
They do not say what we do. They say what we hold to: a person does not have to wait until everything is in place before he is allowed to say of the days in front of him, "this is good."
You can afford to eat and you can go out dressed. What remains is: eat well, dress well.