I know the PSP was designed to be non-expiring but I do add some Aquatabs. They're compact and I rotate them. Should I forget too then I can still try them or just discard them and be no worse off than I was. A few things can be crammed in, especially if a few things are removed.

If nothing else the PSP is/was a great bargain! You could part it out and get the contents for less than they generally cost individually.