With a memory card inserted (to save progress), enter an item shop. Hold L1 + L2 and leave. Repeat the process for more stuff.

Note: They mess up on this cheat it not just L1 and L2. You have to hold R1,R2,L1,L2 when you leave the skill shop. You also have to set a skill or buy a skill for it to save. Thanks to James Arnold for this note.