Travel restrictions?

Just by the way: if you are questioned about your reason for travel, answering politely and truthfully will serve you much better than screaming about violation of your rights. Most officials just want as little bother as possible, and if you seem like a reasonable person they are much  more likely to wave you on.

It is usually a combination of government, health authorities and immigration bureaucracy. There is usually a set of guidelines, but as they tend to be put in place in a rushed manner, they are open to interpretation. 

If international that would be the government of the country you are going to

The governments of the individual nations decides. But the general rule of thumb is that it's for citizens returning to their home countries to wait out the pandemic and those who can prove with documentation that they're traveling for what that given nation has decided can be termed "essential business", and that somewhat varies by country. 

The government establishing the restrictions gets to define what's non essential.

The government gets to decide that.

Basically - if you don't have to do it (ie for the permitted reasons of going out, eg going to school, going to work if you can't work from home, attending a funeral) - then it's non-essential. 

Since this is the Packing & Preparation section, I suggest you see if you can ship yourself in a FedEx box.