Hi!
Just from the top of my head, I would suggest the following:
- 押入れ for closet
- 記念の箱 for box of mementos; 記念入った箱 would be box with mementos, or box in which mementos have been put in. (BTW, しまう would be a good verb for things you keep on a box.)
- …箱があるinstead of 箱はある. Otherwise, it looks like you are saying you have that box in your closet as opposed to other things you don’t (the famous が/は usage)
- 無くした時計 instead of 無くなった時計, because you lost it.
- 壊れたストラップが入っている, が for the reason above and 入っている because the strap is in the box and keeps being there.
HTH!