I don't believe the OP has been fully addressed so I will add my thoughts. Apparently the legionary eagle was still in use at this time, though the other banners and standards seemed to have changed. The legion's flags replaced the spearpoint at the top with the Christian chi-rho symbol, and the standards used by cohorts (I can't remember what these are exactly, are they the ones with the hands?) were replaced by the draco, basically a dragon/animal head with a windsock attached that would look pretty cool when in motion. The legions themselves were organized very differently, and now much smaller. And compared to Caesar's day they contained a much greater amount of non-Italians, most of the army would've been from outer provinces or even "barbarians", and yet for all this the army was no less effective. It was perhaps even more efficient, although the state was still fully capable of enormous screw-ups that got the empire to crumble without having to blame the military. If anything these late armies were the only thing really keeping the empire up despite the best efforts of some emperors to destroy the empire.
As far as equipment goes, I'm not entirely sure on the specifics, but I know a few things. Segmentata was not in use, as you said. I think the typical armor (as it was for the whole history of the empire) was still mail, though scale-armor was used a lot by this time, mostly by cavalry IIRC. Helmets had become more simplified, shields became more oval and later on completely circular, the gladius was superceded by the longer spatha, overall the Romans started to more resemble their "barbarian" opponents. Of course shoes and full trousers were standard by this time. I think the pilum had been generally replaced by the plumbata, and I remember reading somewhere that soldiers would carry five of them and they had a very good range.