Expand Arduino storage without an SD card
This may be relevant if you can get your hand on some old 30 Pin SIMM RAM.

Its a library some clever chap wrote to interface with 30-pin simm ram using an atmega328p on Arduino

https://github.com/zrafa/30pin-simm-ram-arduino

Also his video here: here https://youtu.be/Yah3ViEggxA

It is apparently quite wasteful though as you only get to use 256Kb of the RAM! 

The author also states that "using this kind of RAM will put your Arduino CPU to refresh the SIMM RAM data part of the time. It means that your sketches (programs) could run a little slower than before. Also, we need to use most of the Arduino pins to be soldered with SIMM RAM pins so there will be just few available extra pins for your project."