Traveling by train, in a hop-on, hop-off manner can be expensive. These are a few options to travel cheaper by train:
Day ticket: A day ticket offers unlimited travel for a day.
Weekend free: A weekend vrij monthly subscription for free travels during the weekend and public holidays, only for residents in the Netherlands.
If the above links do not work anymore, search on https://www.ns.nl/en for words like "day ticket", "weekend vrij", "railrunner".
The museum pass is a yearly subscription, which offers unlimited visits to over 500 museums from the Netherlands. The yearly museum pass can be acquired by EU residents, while non-EU residents can buy a temporary card, providing access to 5 museums. More details at https://www.museum.nl/en.
The Dutch cuisine is not known for its diversity, but there are few things to try out:
Sandwiches: You can find good sandwiches at any supermarket, but the best ones are sold by places with the word "broodje" in their name. The sandwiches are prepared in front of you and, usually, the options are diverse (gluten free might be hard to find, though).
Fish: At any market and some other reserved spots in the cities, you will find a fish truck. Usually named "Vishandel" or "Visspecialist", they will have plenty of fish options. The most known are "kibbeling" (battered fish) and raw hering. The best ones are along the North Sea coast.
https://www.wikitravel.org has extensive information about Dutch cities.
Disclaimer: The information provided here is purely informational, based on personal experiences. For up-to-date information, always check the official websites of NS and museumkaart.