In today’s environment of possible active shooter, bomb threat, gas attack threat, etc. it occurs to me that my EDC/GHB ought to have kit to hold open , e.g. a stairwell door so I can go down a floor or two and see if I can open a lower floor door without locking myself in the stairwell. Likewise, I should be able to “Lock “ a e.g. an office or classroom door, that doesn’t have a fitted lock or top mounted auto door closer to tie-up and thereby hold it closed OR by trying to barricade it with furniture. ( Albeit ,I may want to do both ,if possible. )
That’s a tall order for small single-use devices , to carry in a sub- 10lb. EDC/GHB bag. Some considerable reflection yielded me the following answers, although I do not claim them as definitive, nor entirely original:

1) AS A DOOR “HOLD OPEN”: a Google search of “ small plastic triangular doorstops” yielded a pair of inexpensive, 2.75” x .5” , brightly colored , almost weightless , plastic wedges. Inserting them on the Hinge side , between the door and the jam, holds the door partially open, even if it is a self-closing smoke-fire door. I carry two, nestled so they take up 2.75” x.5” of space; and

2) AS A DOOR “HOLD-CLOSE: if their is a self closer at door top of a lock less door, as many videos on the net demonstrate, wrap and tie off the triangular metal arms, to keep them from operating or tie the door handle to an adjoining door handle or sturdy protrusion. If neither of those strategies are available., ( and here is my semi-original idea) ) , resort to the old college dorm trick of “pennying “ the door closed, rendering it inoperable from either side , as long as the pennys are in place. To install, press the door against the jamb or the toungue , with ur body weight, as hard as you can. This will usually create a small extra space between the lip / edge of the door and the metal door jam, mounted in the wall. Fill the gap with two or more stacked pennys and push them tightly into the extra space. It works. I can witness that from being both victim and perpetrator in college. Eventually, if those locked out ram their shoulders or full body kicks, long enough and hard enough to shake the pennys loose, it will give way. But trust me, done correctly, it is sturdy and very hard to dislodge.