Because I'm jealous of your freedom to gallivant after trout for such long periods of time, I'm tempted to leave you to your own devices.... :)
Instead, here are a few thoughts in response to your question:
Baetids--I won't call them BWOs, but these (variously colored) little buggers are among the most significant and reliable mayflies in the late season. Although they have the reputation of being "bad weather" bugs, that's not always the case, especially in the late fall.
Slate Drakes (Isonychia spp.)--A second "batch" can be significant on many streams in September, though they are usually smaller (#12-14) than the earlier ones. I have a special fondness for these fast-swimming critters, so I wouldn't be without an Iso nymph imitation on any stream with good populations.
Tricos--They can linger into early November in some places, though their number (and consequently, their significance) dwindles quite a bit as September rolls into October.
Little Yellow Quills (Leucrocuta spp.)--These little (#16-18) mayflies look like smallish Sulphurs from a distance, but they have two tails and small dark flecks on the forward half of the wings. They usually emerge in riffles and can emerge underwater, so small wet flies often work when the fish aren't taking them on the surface. They are a fairly common and widespread mid-late season hatch, and can linger into October. IMO, they are very underrated.
Autumn Mottled Sedges (Neophylax spp.)--These medium-sized (#12-16) brownish mottled caddisflies are sometimes seen in good numbers in the fall. I usually encounter them on smallish streams, but I don't know if that is typical. The Eastern Box Wing Sedge (Ironoquia spp.) is a rusty brown-colored caddisfly of about the same size or slightly larger that might also be significant in a few places.
Great Brown Autumn Sedges (Pycnopsyche spp., sometimes called October Caddis or Pumpkin Caddis)--These large (#8-10) caddisflies have brownish orange or pumpkin-colored wings, usually with a few dark blotches toward the rear. Most often seen around dusk into dark, I've had the best results with large rusty or orangish imitations of the "pupa." A large Orange Stimulator can sometimes get a good response on the surface in the fall (whether or not that response is related to these caddisflies).
Hoppers, beetles, and ants are standard fare for prospecting on the surface until you get a few hard freezes. As you get later into the late season, prospecting with things like streamers, stonefly nymphs, or small-to-tiny nymphs (that imitate the early stages of some of next year's crop) can be productive. Of course, through the end of October into November and December, you might want to consider imitating what is often the most productive late-season "hatch" on many streams...eggs.