A nice team picture including the coach is always nice. It doesn't have to be huge, I've got some 3x5's in small frames I keep around the office that I still enjoy years later.
I have a softball signed by the entire team that I coached last year which is set on a "golden glove" type trophy base. It is in my office and I see it every day reminding me of the fun we had.
If DD is the only player leaving, as a coach I would treasure a softball signed by her with a note of thanks mounted similarly or even just by itself (which I would mount).
I love Christmas ornaments. I took a wallet size photo of the team, trimmed closely around the team to make the picture smaller, curled it around a pencil, and inserted it into a clear Christmas ornament (creating a ship in a bottle effect). I had to maneuver the picture to press it against the glass. I added Easter grass and stuffed it behind the photo (many types of fillers, confettis, in many colors are available). I finished it off by using glitter paint with the team name and year. Ribbon for the hanger and hot glued a bow made from the same ribbon where the hanger and ornament meet. Memorabilia and has been greatly appreciated by anyone I have made one for (numerous ways to capture a memory...I have my daughter baby picture and a strand of her baby hair in one
I have numerous pictures of my teams and players up in my room. I love looking at them. I also have a few pictures of gifts from players to me. One year, some of my players decided to get me a personal chair. I still have it. I love that chair. I don't know if they ordered from somewhere or if they bought it and had it sewn by some sewing place. It has our team name and Coach Butler on it along with an emblem of the team. It might be something to consider.
That's great! No one will accidentally walk off with that chair One of my students bought me a book bag embroidered with my name on it. Personalized items are meaningful.