A GPS enabled phone - It's easy to get lost in Belgian cities, particularly in the twisty streets of Bruges’s historic center. Pre-load a map on WIFI, then your phone's GPS will keep you right.
A camera - Belgium is almost unbelievably picturesque, and it's home to some of Europe's most incredible buildings. You could fill several SD cards in Bruges alone, so make sure you have some spares!
A waterproof coat - Belgium is notoriously rainy, so don't be surprised if you see a few showers, even in summer!
An adapter plug - Belgium uses European-style 2-pin plug sockets. The voltage is 230V, so you'll need a step-down transformer to use appliances that run on 110V.
Comfortable shoes - You'll clock up some serious miles wandering around Belgium's beautiful cities, and the last thing you want is a blister. Make sure your shoes are up to the job.