What practical, day to day differences are there for work between
contractors and W2 employees, specifically for software engineers?
I know that contractors are paid differently and they don't get
insurance. I'm not asking about that, but instead, how much does it
alter your day to day?
The big difference is in levels of responsibilities. As a contractor I can't tell somebody else to do something. I can ask. I can tell my client what I think needs to be done. But if another contractor or an employee doesn't think my ask is important to their set of tasks, there is little that I can do.
My relationship with the client is dictated by the contract, which I probably haven't seen if I work from another company and the contract is between the two companies. That contract defines my roles and responsibilities.
In the original version of the question there was a list of supposed differences, but in reality the differences between employees and contractors can range from subtle to massive. Both may be allowed to bring their own device, or neither. Both might have to attend meetings, or the two groups can have separate meetings.
One suggested difference is time cards. In my experience everybody: salaried employees, hourly employees, offsite contractors, onsite contractors, have to fill out time cards. This is done to account for vacation, and sick leave, but also to document what project they are working on. In a few situations, I was unlucky to be required to fill out two time cards: one for my employer, and one for my client. Those situations were examples of accounting at the customer wanting to be able to track pay expenses everyday.
One difference is related to social events: the employee can be allowed to charge a special code when there is a company required social event. But contractors aren't allowed to do the same, unless their employer gives them am overhead charge code that reduces the profits of the contract. Or they can take leave. Or they can just not charge for those hours.