Carrying ID in Belgium ...
In Belgium you are required to carry ID at all times. What I always did (as I didn’t like to carry my passport all the time) was carry a copy of my passport and other important ID’s on a piece of paper. I do this around town or when on my bike. Other times I always carry my passport. Your drivers license is not considered ID (as it is in the US), so your passport is your ID here. Always have it when crossing the a border, even within Europe and the Schengen Zone.