I find the post game content a bit overwhelming right now. Got the fully upgraded celestials for everybody exept Auron and Wakka (damn Auroch Reels just won't appear on the damn tournament *sigh*). I guess the next logical steps would be to start capturing some monsters and slowly start building strong armor. But I don't really know where to even start. My armor pretty much sucks ATM, everything is straight up stuff I picked up from the story.
Shit like Ribbon seem like a total bitch to get.
Well the most immediate recommendations I can offer is buy empty 4 slotted armors from Wantz in the Macalania Woods (near the exit to the Thunder Plains) or try and kill Adamantoises and hope they drop one, Obviously getting them from Wantz will be quicker, but costly.
Farm Mimics (Treasure box monster) in Omega Ruins until you have at least 900,000 gil (Rikku with her Godhand will speed things up, as you get 100,000 gil per Mimic so, at best nine encounters at the least)
Bribe Machea in Omega Ruins (or if you caught one, fight 'em in the Arena) for 360,000 Gil and you should get ~60 Chocobo Wings, you need 80 for Auto-Haste on Armor.
After you got Auto-Haste on your empty armors. Try and kill Fafnir in the Arena, he drops 40 light curtains if you beat him, you need 70 Light Curtains to put Auto-Protect on Armor.
Auto-Haste naturally dramatically increases the speed of the wearer, and Auto-Protect cuts ALL physical damage in half and most enemies in the game use more physical attacks over magical ones.
After you can at least achieve these two, then you can try and bribe Ghosts in the Stolen Fayth Cavern for 200,000 gil to get 30 Mega Phoenixes. This adds the ability Auto-Phoenix on armor which is a automatic revive upon death (as long as you have at least once phoenix down in your inventory) also it's instantaneous and does not waste a character turn.
If money is an issue, just sell any weapons and armors you get from killing Arena monsters (notably One Eye and whatever drops you get for farming Fafnir for those Light Curtains)
Those three I find are most useful abilities to have on armor, with Ribbon taking up the 4th and final slot.