Most smartphones these days come with a decent amount of internal storage space to start off with, usually around 32GB, but plenty of devices still come with 16GB, and some come with even less. A lot of these devices come with expandable storage slots though, leaving you room to insert a microSD card to get more storage than you started with. Usually microSD cards with at least the same amount of what your device offers internally can cost upwards of $30 or more. Every once in a while though you can find them on sale, like these two microSD cards from Samsung.
The 32GB and 64GB cards are on sale right now for $11.05, and $21.99 respectively, making this a pretty good deal to at least double your storage. Each card is class 10 which means faster read and write speeds for transfers, with speeds of up 48MB/s. Since these are micro SD cards they'll fit into any mobile device like smartphones, tablets, and handheld gaming systems so long as they're compatible with microSDHC and microSDXC format, which should be most devices these days. You also get an adapter with either card that fits into normal size SD slots, so you can use it with other devices that take standard SD instead of micro. Normally you'd be looking at $38 and $60 for either of these cards, but you can grab them on sale at over half off right now.