USB Memory Stick for RPi

Hi there me hearties,
I have built a time lapse camera with my Pi Zero, Zero Lipo, Pi NoIR Camera, some IR LEDs etc.
The battery is a 2500 mAh and so should last a day or so and the system is set up to take one frame every five minutes. I'm thinking of changing the power source to a mobile phone battery pack which will last for ages but obviously the SD card is going to get full before the battery runs out and so was thinking of using a USB memory stick. Any ideas on how to use it and get the photos to save to that?