Hello Pat! You can remove all the clothing and add free standing metal shelves. This will eliminate have to build shelves and you can easily convert the closet back to a clothes closet any time. You can stack things and use bins. I have a large walk in closet off my dining room. Originally it was for coats and shoes but it is multipurpose now. Coats, shoes, boots, shelves with food and kitchen appliances, husband "stuff", a dog kennel, a filing cabinet! Once a year or so I clean it all out and am amazed how much "stuff" is in that closet!
You could put inexpensive book shelves in it OR shelves on the walls and use it as a pantry. We had done this with the book shelves in one of ours
"L" brackets and shelving board would be the easiest and be able to utilize all the space.
I would start with adding shelves. Paint the inside of the closet and add a light. You didn't mention if it was a free standing closet or a built in. I have a push light in my cupboard to give me some light where there isn't any.