I know this is a few weeks old so don't know if it will be helpful to the OP, but I minored in graphic design in college and have had a few design jobs here and there. Now I've been hiring several freelance graphic designers to help promote my new startup.
As a potential employer, I wouldn't be impressed with your ability to copy someone else's work. Being able to trace an image or logo from a low resolution photo is pretty much a basic skill. I'm assuming by even applying you have the basic skills, I wouldn't want my time wasted by you even showing me that.
The best graphic designers that I have seen ALWAYS start their designs with pencil and paper, not a computer. Design your logo by sketching it out on paper, scan it, then trace it in Illustrator. NOW THAT is what would impress me as a potential employer. Getting a portfolio together is hard work. If you have to take a job flipping burgers and mopping floors for a while longer to get a good portfolio together than do that. I would suggest donating your time and ability to mom and pop shops like others suggested. Having logos that real businesses are using that you designed is impressive to an employer, and the word of mouth advertising you can get can pay off big time. You can also find lots of contests online where you can win real money for your work. Enter some of those.
Using logos like land rover and pepsi in your portfolio could construe the false message that you had something to do with designing those logos. While I would say you would be safe by using it for personal use, it has the potential to convey the wrong message to an employer by making them think you worked for these big name companies, and any good employer is going to be more impressed by your original work, not work you traced. Tracing a low res logo in illustrator is as easy as going to Object > Image Trace > Make...not a skill worth bragging about.
