Voltage converter (220V to 110V) with surge protector power strip—how much wattage do I need, and is it safe?
What are you powering? A laptop power supply for example is usually rated for 100 to 240VAC and 50/60 Hz...

A decent 230VAC to 110VAC transformer (I have one for some power tools) is about £50 so if you are only looking at a few usb devices it would be cheaper to buy usb chargers in the country you are going to.