Keep in mind that if in fact you do not stay with your current employer, you will want to have a generic place holder that represents your highest level acheived. I made the mistake of giving myself a "Manager..." title instead of "Director..." when I was given the oppportunity to create my job title and that created unnecessary obstacles when seeking a job change. The more senior position you can claim the better you will be positioned for salary negotiations and placement with your current or subsequent employer.
After that, let your creativity be your guide. You may want to put an aspirational identifyer in the title. For example, if you are involved in buying but have dabbled in and wish to expand your responsibilities to, for example, logistics, you may want to add a reference to "value chain" in the description. Good luck and you are very fortunate to have been given the opportunity to create your own job title!