Disk-Space Upgrades for PDA

[The Grim Sleeper]

I my experience, PDA's and ROM-carts are the same size: either of them will fit into a box or a uniform chest pocket.
So if you have to choose between carrying around an EEPROM or an extra PDA, the PDA always the better choice: almost the same disk-size, easier to find, can run programs unaided, and can fit another cart inside itself; sure, that cart could be a tricked out EEPROM, but what programs would you put onto that EEPROM that you could not keep on the Extra PDA's drive or find on a normal read-only cart?
Gathering and writing stuff on a EEPROM to the point where it becomes a superior alternative to any normal cart seems tedious and of little value.