To add to the tips above:
💳 Do I need cash in Netherlands, or can I use my card everywhere?
Cash is accepted in most places, as are cards, contactless payments are the standard. There are however some places that will refuse cash, such as public transport. Maestro is the card to use as Mastercard is less accepted (acceptance increases, but it will take a few years). Don't expect other systems like AMEX or VISA to be accepted. Most shops and restaurants display accepted cards near the entrance, the dark blue card symbol with 'PIN' on it usually means they accept Maestro.
🍺 How much does a 0.5L beer cost?
Well, the € 5 figure goes for bars, almost throughout the country and may be higher in touristic areas such as the inner city of Amsterdam. Pitchers of beer are not common and rarely seen in bars. The average price is a lot lower when you just buy your beer (or wine or other spirits) at a supermarket. The most expensive is Albert Heijn, which sells six 0.5L cans of Heineken for € 7, or a decent bottle of wine for a few euros.
🍽 How much does an average meal cost?
€ 15 won't get you a decent meal in most restaurants, unless you count a budget pizza or McDonalds as a decent meal. Most restaurants will charge you € 25-35 for a decent two-course meal with a couple of drinks per person. In supermarkets you can get a decent meal for under € 5 per person, a Big Mac menu will cost you € 6,75 (the Bic Mac-index of the Netherlands is $ 3,79 n september 2019).
Most restaurants, fast food chains and other food outlets offer at least a few vegetarian options, some even offer vegan options. Supermarkets too offer a wide variety of vegetarian meat-substitutes.
🔌 What type of plug do they use?
The voltage is 220-240V, AC at 50-60 Hz. Be aware that most hotel rooms still lack sufficient wall outlets to supply all of your mobile devices. When you bring more than just your phone, be sure to bring an extension cord or a USB-plug with multiple sockets.
🗺 How do I get around?
The cheapest way to get around in cities is walking. You'll see the most of the city that way and city centers aren't that large, so everything is within walking distance.
The second best way is public transport, which is dense in the larger cities such as Amsterdam, Rotterdam and The Hague. Be sure to buy a card in advance that will provide traveling for one of multiple days in advance at a fixed rate as tickets on the vehicle are way too expensive.
Trains have a high frequency and will bring you from city to city in a cheap, fast and comfortable way. They will bring you from Amsterdam to Groningen or Maastricht in less than three hours, being the opposite corners of the country. Rotterdam, Leiden and Utrecht are just half an hour by train and within the hour you'll reach 's Hertogenbosch or Zwolle, which are very nice places to visit too.
Cycling in large cities is for the daring and brave as traffic is quite dense and busy. It is very nice to cycle through Amsterdam, but packs of cycling tourists are infamous because of their lack of attention to other traffic and lack of experience. The other parts of The Netherlands (being mostly flat) are perfect for cycling as traffic is less dense and there are good quality separate cycling paths.
👀 Any other good tips?
Be sure to bring clothes for all seasons as the Dutch weather tends to vary from day to day. In summer the temperatures can rise up to 30ºC (2019 put a record in the books with temperatures up to 41º), while a few days later it can be only 18ºC and rainy. In the autumn it mostly rains with temperatures of 10-20ºC and loads of rain, although an Indian summer in October is not a rarity. Winters are mostly soft with temperatures around 5-10ºC and poring rain most of the time. Spring is nice, with temperatures of 15-20ºC and not a lot of wet days.