These are some minor changes made so that I could use it for commuting.
I have an early morning class (Military science 110) which meets outside for physical training. Running, push-ups and sit-ups mostly. This is an Army ROTC class, but any student can join it for the exercise. Since there is no place to lock up things like my lights and flat repair kits, I added the milk crate with locking lid.
I used 2 old milk crates I had and cut the bottom off of one to make the lid for the other. In the above picture it is locked with just 2 padlocks. I may add more padlocks when I get a chance, but as you see with 2 it opens really easy. Maybe too easy. The crate is attached with several zip-ties. It is very stable and does not move at all.
My main thought is that is a thief can see there is nothing worth stealing they won't bother trying. Also since this bike is mainly out from 5am to 5pm, it may be good hours to avoid the majority of thieves, not sure.
In any case it is always locked up with 2 different locks in a well lit area on campus with lots of foot traffic, so I feel pretty good about it security.
Although it rides pretty well, it can get top heavy. The milk crate with locking top is large enough for most days. On days that I have to carry a few books and my lunch and the bike gear (flat kit, locks, etc) it is not quite big enough. So I am not 100% happy with this set-up, maybe 80% though.
I see many options for further mods to my cargo devices. I could attach side baskets to the rear rack to carry things lower. Maybe even figure out a way to put a simple locking top on those. Or I could use rectangle milk crates for a bit more lockable room, but would still have the issue of weight up high.
Here is a link more information about vintage Treks