Well, just the usual ones. Worth pointing out:
Falcon Horn is a must have, since we cannot fly, it is the only way to pin down those pesky balloons one turn and charge them. Also works on gyrocopters. Yes, Renegade crowns have low leadership. Or do they? Characters have warband, that means their discipline actually increase with rank bonus. More, the knight origin also adds Veteran rule, to reroll that test. A simple captain can easily get to Ld 10 rerollable test to use the falcon horn.
As you pointed out the Errantry banner is crazy good too. And I want to remember: this is not cavalry only. Yes, bretonnians put it on cavalry. But Renegades can use it on veteran sellswords with great weapons (or halberds) and it also works when they are pursuing after a FBIGO. Veteran also mitigates the effects of impetuous, with a rerollable Ld10 test. And it can be carried by the same captain with the falcon horn. Renegade knight on foot with Full plate, shield, great weapon, falcon horn and errantry banner. 167 points.
Still talking Bretonnia, sword of the quest and talisman of protection is 100 points exactly. Good for a Renegade lord on warhorse. Yes, only 3 attacks, so it isn't really a banger, but S7 Multiple wounds (2). And WS 7 means you hit WS 3 on 2+. Great against Chaos spawns, giants, ballons etc. Or you can just use a charmed shield and the ogre blade for multiple wounds (D3), still S7, add a couple gauntlets of the duel to make sure enemy characters don't escape your multiple wounds.
Twin tailed wand paired with Wizard's staff, Demonology lvl 1 mage on horse, in the outriders with reserve move. That's crazy good. You start hidden, then move 8", cast twice the summoning (with a +2 bonus, even at level 1, or you can upgrade to level 3 for a +3 bonus, 60 points tho), then go back to hide with reserve move. Not even Wood Elves can do this trick.
Empire also has a great BSB, Griffon banner, Twice blessed armor, shield, great weapon and ring of taal. Adding a 5+ ward save to a 3+ armor save infantry? Yes please. Casting hammerhand will also give the unis a bit of punch, which is honestly lacking when you aren't using greatswords.