Infinite and Quick Cash Gain:
You can get infinite gil at any time later in the game. It applies any time after you get the GF Tonberry. Have Tonberry learn all menu abilities. You needed at most 100,000 gil (75,000 gil if you have Discount) to have 100x Tents.
- Call an Item shop.
- Buy as many Tents as possible.
- Convert all Tents into Mega Potions (with Leviathan's Recov Med-RF ability).
- Sell all Mega Potions and you receive 187,500 gil.
The exchange rate is 4 Tents = 1 Mega Potion. You will get 25x Mega Potions.

Islands Closest to Heaven/Hell:
These two islands are home to incredibly powerful monsters and lots of hidden powerful Draw Points. They're good places to build levels.
- The Island Closest to Heaven: is near the Chocobo Shrine.
- The Island Closest to Hell: is near Winhill, towards the west end of the map
Land on each island and check your location on the status screen to make sure it says "Island Closest to.." whatever.

Raising Stats:
Doomtrain's Forbid Med-RF can be used to make stat boosting items, but what items are they?
With Tonberry's Familiar command and Eden's GFAbl Med-RF, you can buy items to make HP, Str, Vit, Mag, and Spr Ups from the Esthar Pet Shop:

 10 Giant's Rings > 1 Gaea's Ring  > 1 HP Up
100 Power Wrists > 10 Hyper Wrists > 1 Str Up
500 Vit-J Scrolls > 50 Orihalcons  > 5 Adamantines > 1 Vit Up
100 Hypno Crowns > 10 Royal Crowns > 1 Mag Up
100 Force Armlets > 10 Magic Armlets > 1 Spr Up

Getting enough money for the items is time-consuming, but not hard. Just use the Quick Money trick above. If you have a lot of patience, you can max out all the main stats without Junctions.

Speed Ups & Luck Ups:

100 Cactus Thorns > 1 Hundred Needles > 1 Spd Up 
100 Curse Spikes > 1 Dark Matter   > 1 Luck-J Scroll > 1 Luck Up
Cactus Thorns can be won from Cactaurs. Use GFAbl Med-RF to turn 100 Cactus Thorns into a Hundred Needles, then use Forbid Med-RF to make that into a Speed up.

Curse Spikes are tough to stock up on. Tri-Faces are the easiest enemies to get them from, but they're rare. Anyways, use Tool-RF to make 100 of them into a Dark Matter; Siren must be Level 100 to do this. Then use GFAbl Med-RF to make the Dark Matter into a Luck-J scroll, and finally a Luck Up with Forbid Med-RF.