Offline Data Storage

Hello guys, I would like to build a fitness tracker similar to UP24, I’m really new with Particle.
My question is about storage. For example, with UP24 you can store your activity offline, and then later you can synchronize with your phone and download all this data. Which component can I use to accomplish that? I don’t wanna use a SD card, I’m thinking about the final PCB, I want something very small.

I’ve used a 25LQ080 1 Mbyte x 8 bit SPI flash chip in the 8-SOIC surface mount form-factor. It’s tiny and easily interfaces directly to the Photon/P1/Electron over SPI. It’s also cheap, US$0.31 in single-unit cut tape.