Ok, these won't awe jaded SF readers, but if I could awe jaded SF readers, I'd be writing SF, not hanging around here
Some of these wouldn't really be wondrous items in a Traveller campaign, but for 1939 they would be, and they also would be the kind of mundane things left behind by an evacuating crew:
Handheld scanner. Probably an engineer's tool to help find problems without having to undo panels first. You hold it and it shows the insides of whatever you aim it at. It's set at some fixed distance now, but maybe the players can figure out how to adjust it. You can decide how detailed the image is and what range it is initially set at.
Ration/storage/cargo containers. Disposable stuff to the crew, but nigh-indestructable to 1939 technology. Airtight containers that can survive just about anything the players put them through. Can be several different sizes. Some of the containers may have variable environmental controls able to duplicate different atmospheres or vacuum, if the players can figure out how to use them.
Grav belt. personal anti-grav harness. Can provide all sorts of fun as players try to figure out how it works. An ancients version may be quite a bit different than imperial make. Maybe it's just a wristband that projects a field around the individual.
One of the first things I thought of was a non-mirror mirror. A handheld device that shows your image when you look into it, but it's not a mirror image. More a curiosity than anything else (and stolen from Annic Nova).
3D camera/projector. A staple of SF, but something that 1939 era characters would find wondrous. Maybe it's just a photo-wallet with a few fixed pictures of strange things, or maybe it's a camera as well, if the players can figure out how it works.
The key may not be to come up with new wondrous items, but to describe things in terms that a 1939 character would relate to, not a jaded SF fan. If you do it right, you can describe a palm pilot (or a game boy like CarlP mentioned) in such a way that a player would find it wondrous, and could take a long time to figure out what the heck it is his character just found.