If you've never bothered to buy a new case for the PSP, then you might have wished at some point that the PSP's case had pouches for Memory Sticks and UMDs. If one was to measure the length of the Memory Stick and add a 3/4 inch or so for Velcro, and then measure the width of the Memory Stick and add maybe 1/4 of an inch to provide room for stitching, then cut a piece of cloth that size, one could make a pouch for a Memory Stick. Remember- the back of the PSP's case will serve as the back of the pouch. This could be done multiple times to make room for more memory sticks. The same procedure of measuring and adding could be done for UMD's. The optimal layout for this should be two UMD pouches towards the top and three Memory Stick pouches at the bottom.
Sorry that I couldn't give any measurements- I didn't have a ruler with me at the time. In a little while, I'll post them.