Cheat mode doesn't work unless you have this
First, go down to the options menu, but don't press anything! Just highlight it. Then press: triangle, circle, R1, L2, left, right, square, circle. THEN, and only THEN, can you press L1, select, Triangle. THAT will unlock the cheat mode for invincibility, level select, and debug mode.
Easy kill Destroyer Droids
To easily kill a Destroyer Droid, run up to it while it is rolling and jump in front of it. It should stop rolling. When it stops, jump before it raises it's shields. When you land, do the spin attack. Do this a few times and it will be destroyed without you losing much health!
Health Pack in the Swamps of Naboo
On the second level The Swamps of Naboo when you get to the little place with all the Gungan frogs go to the left of the grass and you'll find a trail that ledds to a big health pack.
Cheat mode...