Grocery stores in the Netherlands are usually very small and only sell one kind of food (meats, breads, etc), but you can find some big ones, like Hoogvliet, Super de Boer, and Aldi. These grocery stores are organized very differently than in America. They organize their food in different sections based on the type of food. For example, the Mexican foods are all together. This is dificult because you could have rice in two different sections, with the Mexican food and with the Chinese food. Why is this? I'm not sure, but we did come up with a theory. The Dutch go grocery shopping almost every day because not many have cars, so they can only bring home as much as they can fit in their bags. This means they usually only buy basic food and stuff for that night's dinner. So, this way they don't have to go searching around to find the different parts of their meal. They can go directly to the section with the kind of food they want to make that night and find all the parts in one place.
When you walk in, the first thing you should do is get a cart. Be sure to bring a guilder along because you have to pay to get the cart, but you do get it back when you return it. In most stores they usually have a fruit section in the front where you have to take your fresh fruit to a weighing machine. There you put your food on the scale, press the button with the picture of your fruit on it, and press "Bon," which means reciept. You will then get a sticker that has how much your food costs and you stick this on the bag of fresh fruit. Some of the big Dutch specialities you can buy here are crokets (breaded mushy meats), vla (a sort of pudding), and french fries with mayonaise. They seem to really eat a lot of creamy pastery stuff and fried foods. The main beer that they drink is Heineken (there is a Heineken brewery close by, so it is easy to get and cheap).
The Dutch also shop at the market, which is on Wednesdays and Saturdays in Leiden. The market on Saturday is a lot bigger than the one on Wednesday and there are lots and lots of stalls to buy different types of food and other stuff. For instance, you can get nuts, fish, chicken, cheese (the cheese stalls smell VERY strongly, as do the fish stalls), fruits and vegetables, bicycle accessories, clothes, flowers, etc. You might want to look at different stalls to compare quality and price because some stalls are better than others. You can also buy Indonesian fast food and french fries at the market if you get hungry while you shop.
At Hoogvliet you can also usually buy what you want, but be careful because some of the other grocery stores might not have what you expect because they don't refresh their stock very often.
An important thing to know in Dutch stores is that they round to the nearest five. For example, if your food costs $23.46, they will round it to $23.45.
"Let Op Zakkenrollers" means "Look out for pickpockets." Make sure to do this at the market!
Make sure to bring lots of bags or you'll have no way to get your stuff home. If you forget you can get bags, but you have to buy them and they are expensive.