If you are asked to make a cake with a specific brand, such as a purse or car, are you required to do anything? or is it legal to use their labels or logos on the cake?

You can create your own copies of labels or logos (with fondant/gumpaste/etc) as long as you get the permission of the copyright owner first, otherwise it is copyright infringement. If you can find a licensed cake topper with the label or logo in question, you do not need prior permission since the copyright owner has already sanctioned the product.

Thanks! That was very helpful.