The most basic Ancient technology takes the form of potsherds: bits of container, small pieces of smashed items that can be pieced together. Things like broken bits of jewellery, rubble that used to be masonry, things like that. Straps, hooks, connectors - the Ancient version of Velcro and buttons. But made of marvellous materials, the composition of which the Imperium couldn't even begin to guess how they were made.
Something like finding a genuine Roman artifact, only made out of PVC or modern memory metal of the kind they use in fancy spectacles. Actually, finding a set of spectacles of clear Roman origin dating from 10BC would be a typical example.
Next to the equivalent of finding the equivalent of Assyrian Scotch tape are things like the remains of warrior helmets, broken armour, clothing and items like that. Items which provide an indication as to what the species may have looked like. Imagine finding a pair of spectacles dating back to Ancient Rome, or a Pictish ballpoint pen. Even the absence of a kind of Artifact could indicate something about the species: for instance, if no Ancient archaeological dig ever found anything resembling a flight of stairs, a ladder or indeed any kind of doorway on the ground floors of buildings, it might indicate something about the Ancients - namely that they may have actually been a race of beings that could fly ...
Archaeologists would kill for Artifacts which carried on them anything resembling depictions of Ancients, or any kind of Ancient writing. Genuine Coyns from the Ancients' time, as compared to modern Coyns used by the Droyne today, are most prized because they seem to virtually be the only actual known Ancient writing system extant. Almost as if the Ancients never wrote anything down, but kept everything in their heads with perfect memories ...
And then there's the high tech stuff the player characters would want, like disintegrator pistols, endless antimatter batteries that never run dry, psionic telepathy amplifiers, grav propellers the size of water biscuits that can propel humanoids through the air twice as fast as an Air'Raft, and so on. But that stuff should be rare; the stuff of legend.
The LBB Adventures Twilight's Peak and Secret of The Ancients went into greater detail on this topic.