So your phone maker thought you could get by with only 16GB of internal storage, eh? You could get a microSD card for some phones, but that's not always supported. So a USB drive with an OTG cable? What is this? The middle ages? You can get a Corsair Flash Voyager GO USB 3.0 drive with a dual microUSB/USB plug built right in – and they're on sale today.
The Corsair drives can be had in three capacities: 16GB ($17.99), 32GB ($22.49), and 64GB ($44.99). All three are available on Amazon, but the 32GB is also on sale through Newegg for the same price (with promo code EMCPFHF72) through 4/30. There is a single plug, but it works in standard USB ports and the microUSB on Android devices.
These USB drives are similar to a number of other products like the Leef Bridge 3.0, but the sale prices make the Corsair drives quite a bit cheaper at the 32 and 64GB levels. Want in? These drives should work automatically with most phones and tablets, with the exception of Nexus devices.