In other words Yedida and all gentiles, don't do what isn't for you, cause you ain't a legal Jew!
Now to the OP.
Yes, at first glance they sound simple and were,........................ back then.
However today it is a much different story. And is not straightforward at all.
For instance many of the kosher laws have to do with idolatry, which many say is dead today, but it isn't.
Let me list a few things to help you to understand where hidden trief or unkosher things can be that you can ingest.
Hair in your bread -
L-cysteine comes from human hair. This hair source can be from offerings to idols in other countries and bought from the temples of these idols. That is why all bread goods, even just a plain kind, needs to have a hecksher. Also be baked in a kosher bakery or one certified kosher by the local Rabbinic. They would not only inspect the ingredients, but also turn on the ovens to make it kosher.
Castoreum - in many of your foods, what is it? secretions of the anal glands of a beaver, an unclean animal. It can be found in drinks and candies as well as other things, not clearly marked on the packaging but under the umbrella of 'natural flavoring'. That heading of NF is also used to hide pork fat in things like tomato sauce too.
Lard - In your maple syrup. What?

Yes, even Maple syrup labled 100% pure could be contaminated with lard as in some processing plants, lard is used to grease the equipment to keep the syrup from sticking as it's bottled.
Lard - On all your food, What?:o How?

By using Aluminum foil to store your foods, this too can be processed on equipment that uses lard to keep the rollers greased. Look for the hecksher on the Aluminum foil. Reynolds is usually always certified. This goes for the aluminum pans for take away meals too that you may get in the store to cook in our receive for a take- out meal.
Bugs and mice etc - These can be hidden in prepared foods, and the government accepts a certain percentage allowable.
Both of these things are unclean for sure, so all foods need to be certified with this in mind.
Are you starting to see where it is difficult? It is not that things have changed regarding what we can eat, but how the industrial revolution has distanced us from growing our own food, thus having control over it from start to finish.
There are many more things but that should suffice to get you started.
There are things like vitamins, medications, OTC and Rx, as well as mouthwash, toothpaste, etc that also have to be scrutinized.

Whew!
Shabbat Shalom