Many of the bakfiets in Leiden are nicely decorated... I thought it was a DIY thing, but no, like the customized garbage bin stickers, it's a BIY thing. I found a nice website where you can pick your bakfiets and see what options are available. There's also a "design your own" (eigen ontwerp) section which, perhaps, is the new DIY.
And they sell matching stickers for crates!