The new iPad Pro models have a USB-C, so you can attach keyboards and other accessories to them more easily. What about older iOS devices? These 3 Lightning to USB OTG cables for iPhone and iPad can help:
USB Camera Adapter for iPhone: this adapter lets you attach keyboards and cameras to your iOS devices. Makes it easier to share photos between your devices.
iOS Lightning to USB OTG Cable: this cable plugs into your iOS device and lets you connect HID, MIDI, and camera devices to your tablet. It supports devices that draw 100mA or less power.
Adwox Lightning to USB Adapter: allows you to connect cameras and keyboards to your device. Just make sure you run the right version of iOS on the right device to use this adapter.
Have you found better USB OTG cables for iOS devices? Please share them here.