Finishing Chapter 19 has the biggest amount of mapwork in a single go. First, we spawn the Lagdou Ruins, the second optional dungeon (Tower of Valni being the first) and the place to go for ultimate endgame content. We will not be touching it.
Second, we spawn Melkaen Coast, and a route from it to Port Kiris. This is Eirika's originally intended route to Rausten, but the Ghost Ship and "Innes being in danger" sent her south to Jehanna instead. Skirmishes that happen to be on Melkaen Coast are far harder than those on the maps we've already played.
And finally, Darkling Woods, the final area of the game. Once you enter that place, you can never leave until you beat the game. Prepare wisely.
And of course I get stuck at Rausten Hall. There's a Melkaen spawn, and I considered showing it, but it's not really that worth it.
I start off by selling anything that's not seeing use. Vulneraries are long outclasssed by enemy risk and I'm amazed I never got rid of them sooner, but right now they're just filling the convoy up.
Now is also the time to sell your anti-armour and Swordslayers. Chapter 19 was the last hurrah of the human classes, and whether you play the postgame or not, the only thing you have left to fight are monsters and the two named character mages. No monsters have the Armour trait, so anti-armour weapons are pointless. Anti-cavalry is still good for Tarvos.
(You can find Thieves in Lagdou Ruins, but usually only, like, one per map.)