Getting the Zodiac Spear without a guide would be virtually impossible. You'd have to be either very negligent about opening treasure chests, or exceptionally lucky to get it from that chest where it's got one chance in a thousand of randomly spawning.

But aside from all that... most of the stuff could be found quite easily without a guide. I used guides as little as possible for the Hunts, only resorting to hints when I got bored or frustrated with dicking around in enormous, difficult dungeons looking for something elusive.

However, without GameFAQs, I'd never have known about the fishing mini-game. Not that I ever play that anymore, anyway...