When I taught Strategic Management at the local university, I was known as a tough professor, having business seniors do thorough case analysis and present it in front of the class. Some students had coasted through classes up to this point and didn't like the rigor of my class, so I would defend why these critical reasoning & communication skills were essential for them. Privately, one of my students said to me, "you are the leader of this class, so when you respond to a student complaint, you are saying that it is important." It really landed with me. I feel that has some applicability here.
My suggestion would be to keep it simple. Don't draw attention to something that you already feel you will have to defend, or you feel will diminish the perceived value of you as an applicant. A resume isn't an autobiography or a confession; it's a marketing document and you have the right to leave things off. You're not being dishonest, you're focusing the adcom's attention on what will put you in the best light.
My recommendation would be to just stick with the name of the company and the value you delivered there. I see no reason to get into the whole part-time job situation *unless* there is a job in there that 1) demonstrates leadership, collaboration, and/or problem solving in a unique way, that you could discuss in your essays or 2). relates to your career goal or helps connect the dots to your post-MBA career goal. Otherwise, I really see no reason why you should include waitressing at Denny's or whatever on your resume.
As for the 3-month job where you were laid off, same principle. Unless the gap is more than a year, or this job is something you want to do in the future, same deal. You may need to explain the situation in the additional info section, but on the resume, there's no need IMO.
Hope this is helpful and good luck!
Farrell