So, you've got a lot of stuff that doesn't fit on your phone? If you're lucky enough to have a microSD card slot, that's easy to fix. Amazon's Gold Box deal today features Sony flash storage, but not just microSD cards.
The main event is the trio of microSD cards—16GB ($7.99), 32GB ($11.99), and 64GB ($25.99) They are discounted by 47%, 52%, and 42%, respectively. If you want to mess with USB OTG, there are regular flash drives, but better suited are Sony's microUSB drives for smartphones. These come in 32GB and 64GB sizes for $14.99 and $29.99.
Everything on the list should have free Prime shipping. As with all Amazon Gold Box deals, this one is today only. Make your decision quickly.