I've worked at places where monitored everything. They had to - it was a legal liability thing.
If you are on someone elses network, they know all about your traffic. If they have enough resources, they can even see inside HTTPS traffic.
Don't use work networks for non-work things.
Use your cell phone data connection if you can't just stop. Wifi is easier to track than wired. Doesn't matter if they use WPA2 or RADIUS authentication. It is their network. They can see all the traffic.
The only way that I'd do anything the bosses might not like is by:
* using my non-Windows systems - never theirs.
* using an ssh/OpenVPN connection that uses IP addresses only. Most smart companies block all VPN stuff.
TOR is not easy to use in a secure manner, though it may be good enough for smaller company networks, if you use your own equipment.
Assume your screen is being captured every 20 seconds and that security can watch live if you use a company-provided box on their network. I've seen this. A security guy watched suspects as they spent 10 hrs at work day trading stocks. He wondered when they actually did their jobs.
For your personal box, they can see all the network traffic, which means that websites you visit will be known if you do not take extra steps. There is good news. If you didn't have to setup a company Certificate to get on their network ( shame on IT for that ), then your HTTPS traffic content is probably safe enough, but they probably have a transparent proxy looking at all other unencrypted traffic.
In very large enterprises, HTTPS traffic can be spoofed with a combined DNS/proxy setup. Use HTTPS-everywhere and Certificate Patrol from your home internet connection to store "known good" HTTPS connection before going into work to see if the company gets in the middle or not. Certificate Patrol will tell you if a different Cert than expected is encountered.