What are the PSP accessories must haves?

Have just bought a base pack PSP, and didnt realise that it doesnt come with a lot of stuff. What's the 'must haves' for the PSP and where is the best place in the UK to buy ythem?

get memory stick,case,screen protectors,psp accessories.

how to put cso parts into the psp?

i download secret agent clank, and it is three parts and they are cso so you can't extract them if it is a cso, so i draged all of them to the psp folder ISO and when i go on game on my psp it does not show secret agen clank so can you please help how to put cso parts into the psp.

it wont recognize if you dragged all the file to iso folder you have yo put all the cso in a folder just create one then click on one of the cso then attract the cso image to the iso folder - psp parts.