While not all smartphones and tablets have expandable storage support, for the ones that do it's a good idea to pick up a micro SD card to increase the amount of storage space that your device has, especially if you tend to install a lot of apps and games and other types of media like music, photos, and videos, as they can take up a lot of room.
SanDisk cards are some of the best quality cards you can buy if not the best cards you can buy, but that quality usually comes at a price and even more so if you pick up a card with a ton of space, like this 128GB card, for example, which normally costs $79.99. Right now though you can pick it up on Amazon for just $44.90 as Amazon is having a sale on it, making this card more than half off, which is a steal for that amount of extra storage space. This is a "made for Amazon" exclusive card for the Amazon Fire tablets and Amazon Fire TV, but that doesn't mean that it won't work with other devices. On the contrary it works with any device that will accept a micro SD card as long as that device will support cards with this amount of storage.