Re: Dutch streetfood.

Certainly would recommend trying the herring (with onions) otherwise you might try 'Kibbeling' which is a Dutch snack consisting of battered chunks of deep fried fish, commonly served with a mayonnaise-based garlic or tartar sauce or 'Lekkerbekje' (deep-fried cod). You can find it all in a fish stand.

Other possibility would be visiting a snackbar
Try a 'patatje oorlog' the sauce is a mix of mayo, sate sauce and onions and it translates to war chips with a 'frikandel speciaal' (sort of minced hot dog with curry, onions and mayonaise)
Another (new) popular dish you will find at the snackbars is Kapsalon (fries, topped with döner meat, grilled with a layer of Gouda cheese until melted and then subsequently covered with a layer of dressed salad greens. The dish is often served with garlic sauce and sambal,)

You might also bump into a 'Oliebollen/poffertjes' stand or 'gebakskraam'
You will find Poffertjes (small, fluffy pancakes made with yeast and buckwheat flour served with powder sugar), oliebollen (dough diep fried usually with raisins etc and served with powdered sugar) and other fritters

And of course there is that freshly made stroopwafel (syrup waffle), there is one stand at the albert cuyp markt (Dovster mentioned he likes markets)