The easiest, no investment of cash, process IMHO is a place called CafePress.
All you have to do is open a CafePress store, create the design in a JPEG format, submit the design, select what items you want the design printed on (T-Shirt, Ball Hat, Mouse pad, Coffee cup, etc., lots of different types of items), set the mark up above the CafePress minimum (can be ZERO markup, which is what I do). Give out the web address of your CafePress store and you're done.
A buyer orders whatever item they want from your CafePress Store and pays CafePress.
CafePress makes the item after the order is paid for and ships the item to the customer.
There is no inventory to get rid of, because there is no inventory. This is a make it when it is ordered type of deal.
Even if no one ever orders anything from your CafePress store, there is no cost.
I've done this for at least 10 years for my forum members.
Works great and I don't have to deal with anything.