Well, people food is not overall bad for dogs. But feeding only people food will result in deficiencies of some things dogs absolutely need for health. Dogs are not people and so won't thrive as best as they can if only fed people food. And that not-thriving brings disease and vet trips. Also, as stated above there are kinds of food people eat that are truly toxic to dogs (not just chocolate).
If a person is going to cook food for their dog or feed raw, the only way to do it is to become very well versed in dog nutrition. You can't just cook up some meat and veges and all is good, despite what you see on YouTube. You need to add supplements and know exactly which ones and then understand the proportions that you need with how much of this or that thing you put into the cooked food in order for the supplements to be at the right levels and so on. It is more complex than probably most people in van life want to do.
The best thing to do is choose the best quality dog food you can afford regularly (see
https://www.dogfoodadvisor.com/ for excellent information on which commercial dog foods are good and which are lousy and clear analysis of why), and then supplement that with small amounts of whatever human food is healthy and the dog likes.
For instance you can use a little of your meat as a topper on a meal. Also good toppers: hard boiled eggs, yogurt, a tiny bit of cheese, bits of cooked chicken breast, a bite of your burger, apple slices, etc. Just do the research so you know what
not to let them have. Like grapes, which will kill a dog eventually if fed to them.
Don't just give supplements to the dog because you think you should or because of an ad you saw. You could be overloading a dog with something they already have plenty of in their food and cause more problems than you solve. Overloading certain things, like calcium, causes a lot of problems. The only supplement that I think is pretty much across the board useful is salmon oil, especially for any dog over 10.
I understand wanting to share with the dog. I do it. But my dogs are trained to wait politely for me to give them the Last Bite. Bit of toast, last bite of the banana and so on. And they can look at me while I am eating but not at anyone else while they are eating because that would be rude.