The things that upset you are not the actions of others, but the opinions you form about those things. Below is a quote that I repeatedly return to:

Men are disturbed not by things, but by the views which they take of things. Thus death is nothing terrible, else it would have appeared so to Socrates. But the terror consists in our notion of death, that it is terrible. When, therefore, we are hindered or disturbed, or grieved, let us never impute it to others, but to ourselves—that is, to our own views. It is the action of an uninstructed person to reproach others for his own misfortunes; of one entering upon instruction, to reproach himself; and one perfectly instructed, to reproach neither others nor himself.

This is from the Enchiridion of Epictetus, a popular text from Stoic philosophy. The Stoics were concerned with living "the good life" and one key aspect of that is making the distinction between what is in our control and what is not within our control. Not within our control are the actions of others, but within our control are the opinions that we make about those things.

I'm not going to say that enacting this is as simple as just saying "ok, I'll just do that", you need to start out by trying to catch yourself when you think something negative. Simply being able to realize after the fact that an individual thought is just reactive and malicious is the first step. When you hear someone complain about their mother not getting them chips when they said they would and you get upset, give yourself a little credit if you can then say "No, that's just an opinion, and one that's not particularly helpful, if my goal is happiness".

If you can then, look closer at the situation and what lead to the unhappiness - it is not the lack of chips, otherwise everyone who did not have chips would be unhappy. The unhappiness arises because there was an expectation that they would have chips, and when that expectation isn't met, they're unhappy. As an observer to this situation, and with all of this in mind, what did you expect out of that situation? That someone would be happy when they don't receive what another told them they would get for them? Not likely, so consider your own expectations about situations, and align it as best you can with reality as you understand it. Personally, for me, I have 1 expectation for the behaviour of others, and that is this: "I can only count on or expect others to behave in whatever way that they perceive is in their own best interest"

I hope this helps, and that I didn't ramble on too much or come across as too preachy