Worth noting that all imps have SPI flash storage available; the SPI flash attached to the imp has some area reserved for the system (upgrade staging, etc) but in all cases there is space available for the user.
There are helper libraries, eg https://developer.electricimp.com/libraries/hardware/spiflashfilesystem
imp006 also has really really low shallow sleep power consumption, which means you can hold hundreds of kB of data in RAM (ie just standard squirrel objects) whilst taking tens of microamps and being responsive to timer or GPIO wakes. See https://developer.electricimp.com/resources/sleepstatesexplained - many 004 and 006 customers use this mode instead of deep sleep as it’s a lot more convenient.