If I were Trump I would have boxes like that for luggage and for onboard snacks and meals.
Sheesh, when I house sit at my son’s for a week, I take one of those boxes with some work projects. I would imagine that Trump would need a few more than I do. How many law suits is he involved in? Lawyers may have sent him documents to review. A couple of years ago my husband and I were potential witnesses in a civil case. Lawyers for the guy suing sent us about 6 inches of documents. Boxes could contain material for a book (or books) he might be working on.