So, what I used to do was bring my own food that was healthy and I would eat with my coworkers when they did this so i could build friendships without killing my diet. I was the same way, they were all thin and I am fat. I would bring healthy snacks on days when I knew there would be birthdays, and I took walks at lunch instead of eating with them. But I invited people on my walks with me. I was lucky that I have a service dog so I always used the pretense that lunchtime was his walk/break time.

But I would mention to the boss that these multiple cooking engagements are getting in the way of productivity and maybe there should be some parameters and when and how long they can do it for. It sounds like a weekly thing with your company and that's just unacceptable. My company regulated lunchtimes very carefully, so I don't know how these temps are getting away with taking long breaks to go shopping and then make and eat food. How are they getting any work done? I would definitely just mention, tactfully, to your boss that it's affecting productivity.

Seesaw