I will be purchasing backpacks that bear no logo or brand in small quantities, and selling them under my companies name.
Based on your very few facts, I see no problem.
The above is general legal and business analysis. It is not "legal advice" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here.
It depends on what kind of agreement you are thinking about. You could enter into a purchasing contract. It is mainly to limit your liability from any manufacturing defects or other quality control issues. Based on the limited information, you don't need a contract to place your companies name on it.