He clearly has poor frustration tolerance and needs help learning not only that, but how to communicate and regulate his emotions more effectively.
While this resource was mentioned with younger kids in mind, the Exercises to Improve Regulation section applies to every age:
Another applicable article with good strategies:
And think about how you can help him not lose his things to often. Many adults with ADHD have an area by the door where they put everything they need every time they leave the house: glasses, keys, wallet/purse, backpack, shoes, jacket, hat, gloves, etc. Then there’s no searching for these items — they are always in this landing zone. You could even take it a step further and make tape outlines of the objects that should go there, to prompt him to leave those items in that area.
In my house, right inside the door we typically go in and out of, we have big hooks for jackets and small hooks for keys, baskets for hats and gloves (one for each person), a small console table with plate and bin for loose items, and shoes and backpacks go underneath that table.
ADDitude Community Moderator, Parenting ADHD Coach & Author, Mom to teen w/ ADHD, LDs, and autism