Xenogears

Lahan Well Items:
In Lahan, at the start of the game, jump down the well a few times. You'll get an eyeball, to sell for gold, an Aquasol S, a Power Ring, a lot of puns and a chill.

Secret Gear:
In the Battle Arena at Kislev, put on special mode one. Go to 'Bonus Battling'. Put the options on three rounds, and hard difficulty to get secret gear (Argento).

Audio Test:
When you are in the Yggsdrasil, go to the control room and talk to the control man. Choose the top selection for a sound test. He'll keep asking the same question over and over. Select the first choice again for a new sound.

Quick Gear Change:
When you are on the world map or a place that you can use your Gears, press L2 + R2 and you can go in and out without going to the menu.