Legal Question in Intellectual Property in Texas

Yes you can put their items in your shadow box without covering them--PROVIDED the items are legitimate and not fake. So, you could have a little bag of Millstone coffee, provided the bag is authentic Millstone (R) coffee. (MILLSTONE is actually a trademark of Folgers)

If, however, you advertise your shadow box as a "Millstone coffee shadow box" or FOLGERS shadow box that would be implying the box is licensed by THE FOLGERS COFFEE COMPANY (which also owns the MILLSTONE brand name for coffee), which apparently is not the case. So, say your trademark is TSBC (Texas Shadow Box Company), you could advertise "TSBC brand shadow boxes containing authentic Millstone coffee", but could not advertise "Millstone shadow boxes". The former is truthful (if it contains authentic Millstone coffee), the second could be claimed by Folgers to be unfair competition (false and misleading) and infringement of their famous "MILLSTONE" trademark, especially when it contains a bag of their coffee. A gray area would be a "MILLSTONE shadow box" not containing MILLSTONE coffee or other MILLSTONE products of Folgers, since there are other registrations for MILLSTONE for other products.