Due to the Raspberry Pi has 4 USB ports, have you ever thought hook up 4 USB devices on it? So you will need a USB extension device such as USB HUB if you want to connect more USB device, but most of them are not for mobility. Now this supply& USB HUB can meet your mobility requirement, it is small and functional. In general, it is multifunctional. You can charge for your cellphone (include iphone), Raspberry Pi 3 Model B/ Pi 2B/ Pi B+/ Pi A+/ Pi B/ Pi Zero. There are 4 USB-DATA ports on the board in case you need a USB HUB as well.