Brussels, Bruges, Antwerp, Amsterdam

In Amsterdam there is a Sandeman's free walking tour and they take the group around the city and introduce you some interesting and offbeat culture/history. Its a fun activity!
http://www.newamsterdamtours.com/daily-tours/new-amsterdam.html

Definitely rent bikes and just ride around the city and breeze thru Vondel Park.

For Amsterdam: Apple Cake

http://foodnouveau.com/2011/10/destinations/europe/netherlands/a-deep-dish-apple-pie-amsterdam-style/

Also really important: In Antwerp you must must must go to the little bakery 'Goossens' (Also in the neighbourhood 'Wilde zee') They have amazing breads (try the chocolate one or on friday the Van dyck with apples) or one of the danish. The best!

Ah and in Antwerp you should go to the neighbourhood the Wilde zee. There you should go for lunch at Lombardia (try the ginger tea that Starbucks wanted to buy but the owner refused :-)). And go for a authentic Brussel Waffle to desiree de lille.
In amsterdam you should visit the Albert Cuyp market and have lunch at The butcher (http://www.the-butcher.com). The Anna Frank house is also a must but go on time because there is always a long queue.
In Bruges (or Antwerp) you should definitely get some chocolates at the chocolate line (http://www.thechocolateline.be ) . You can buy the best chocolates there from the chocolatier that was voted the best in the world and who works together with Pierre Hermé.

I live in antwerp and I would definitely would say that roji is my favourite place ever for diner. In Amsterdam kinnaree, the best thai food in Europe

We ate at De Kas in Amsterdam several years ago and it was pretty amazing:

http://www.amsterdamtips.com/tips/de-kas-restaurant.php