So how do I make Gil end game without a crafting or gathering class?

[Egonomics]

Short answer: You don't.

Long answer: You don't, because gil fountains in this game are inexistant, even for crafters. Crafting will only give YOU personal wealth, while you take it away from another player. While this is the only way to keep yourself "fed" for a while, this will come crashing down soon enough if not addressed.